HomeMy WebLinkAboutCT 2018-0002; AVIARA APARTMENTS; PRELIMINARY GEOTECHNICAL EVALUATION; 2016-07-07PRELIMINARY GEOTECHNICAL EVALUATION
9.2 ACRES, APN 212-040-56-00,
LAUREL TREE LANE AT AVIARA PARKWAY,
CARLSBAD, SAN DIEGO COUNTY, CALIFORNIA
FOR
SUMMERHILL HOMES
2 VENTURE, SUITE 360
IRVINE, CALIFORNIA 92618
W.O. 7103-A-SC JULY 7, 2016
Geotechnical C Geologic C Coastal C Environmental
5741 Palmer Way C Carlsbad, California 92010 C (760) 438-3155 C FAX (760) 931-0915 C www.geosoilsinc.com
July 7, 2016
W.O. 7103-A-SC
Summerhill Homes
2 Venture, Suite 360
Irvine, California 92618
Attention:Mr. Kevin Doherty
Subject:Preliminary Geotechnical Evaluation, 9.2 Acres, APN 212-040-56-00, Laurel
Tree Lane at Aviara Parkway, Carlsbad, San Diego County, California
Dear Mr. Doherty:
In accordance with your request and authorization, GeoSoils, Inc. (GSI) is pleased to
present the results of our preliminary geotechnical evaluation of the subject site. The
purpose of our study was to evaluate the site geologic and geotechnical conditions relative
to the residential development proposed thereon, and to provide preliminary
recommendations for earthwork construction and the design of foundations, slab-on-grade
floors, and driveway pavement.
EXECUTIVE SUMMARY
Based upon our field exploration, geologic, and geotechnical engineering analysis, the
proposed residential development appears feasible from a soils engineering and geologic
viewpoint, provided that the recommendations presented in the text of this report are
properly incorporated into the design and construction of the project. The most significant
elements of our study are summarized below:
•In general, surficial earth materials units at the site consist of undocumented
artificial fill, roadway fill, underlain by alluvium (encountered on the eastern parcel
only), and in turn underlain by bedrock of the Santiago Formation. The upper
approximately 1½ feet of the Santiago Formation is weathered.
•Due to their relative low density and compressibility, all undocumented fill, roadway
fill, alluvium, and weathered Santiago Formation are considered unsuitable for the
support of settlement-sensitive improvements (i.e., residential structures, walls,
pavements, etc.) and/or new planned fills in their existing state. Based on the
available data, the thickness of potentially compressible soils, excluding roadway
fill areas, based on the available subsurface data, remedial grading excavations are
anticipated to extend to depths on the order of 17 to 20 feet below existing grades,
on the east parcel, and about 3 to 7 feet below existing grade on the west parcel.
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However, localized thicker sections of unsuitable soils cannot be precluded and
should be anticipated. Conversely, the underlying unweathered Santiago
Formation is considered suitable for the support of settlement-sensitive
improvements and new planned fills. In order to provide uniform support of
settlement-sensitive improvements, all undocumented fills, roadway fil, and
weathered Santiago Formation should be removed to expose the underlying,
unweathered bedrock (Santiago Formation). The excavated soils may then be
reused as engineered fills provided they are relatively free of organic matter and
deleterious debris prior to placement, and prepared in accordance with the
recommendations in this report. Alternatively, the proposed residential structures
may incorporate deep foundations and a structural concrete slab-on-grade floor.
Please note, if the latter is selected, any ancillary site improvement (i.e., walls,
hardscape, etc.) not supported by deep foundations or a structural slab may be
subject to settlement and resultant distress.
•It should be noted that the 2013 California Building Code ([2013 CBC], California
Building Standards Commission [CBSC], 2013) indicates that the removal and
recompaction of unsuitable soils be performed across all areas to be graded, under
the purview of a grading permit, and not just within the influence of the proposed
improvements. Relatively deep removals may also necessitate a special zone of
consideration, on perimeter/confining areas. This zone would be approximately
equal to the depth of removals, if removals cannot be performed onsite or offsite.
Perimeter conditions and existing offsite improvements will limit the removal and
recompaction of potentially compressible soils near the margins of the site. As
such, any settlement-sensitive improvement at the property line would require
deepened foundations, additional reinforcement, or would retain some potential for
distress and therefore, a reduced serviceable life. The limits of the proposed
remedial grading are indicated herein. On a preliminary basis, any planned
settlement-sensitive improvements located approximately 17 to 20 feet from the
property line on the east parcel, or within about 20 feet of the roadway fill would
require deepened foundations or additional reinforcement by means of ground
improvement or specific structural design. This should be considered during
project design, planning and construction. This condition should be disclosed to all
interested/affected parties should it exist at the conclusion of grading.
•Visual classification and expansion index (E.I.) testing, performed on representative
samples of the onsite soils, indicates expansion indices ranging from 32 up to 72,
with the potential for the occurrence of even higher E.I.s. Thus, the expansion
potential of the onsite soils ranges between low and medium, to perhaps highly
expansive. Based on the available laboratory data, some of the near-surface, onsite
soils meet the criteria for expansive soils, as indicated in Section 1803.5.3. of the
2013 CBC (CBSC, 2013). In order to comply with 2013 CBC requirements for the
mitigation of expansive soils, the proposed residential structures will need specific
foundation and slab-on-grade design that will tolerate the shrink/swell effects of
highly expansive soils (see Section 1808.6.2 of the 2013 CBC). Alternatively,
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expansive soils within the influence of the proposed residential structures may be
removed and replaced with very low expansive soils (E.I. less than 21) with a
plasticity index (P.I.) less than 15 (see Section 1808.6.3 of the 2013 CBC), reducing
foundation requirements.
•Laboratory testing indicates that tested samples of the onsite soils are: medium acid
to slightly acid with respect to soil acidity/alkalinity; severely corrosive to exposed,
buried metals when saturated; present a negligible (“not applicable” per American
Concrete Institute [ACI] 318-11) sulfate exposure to concrete; and have low to
slightly elevated concentrations of soluble chlorides. The use of concrete
conforming to Exposure Class C1 in American Concrete Institute (ACI) 318-11,
should be utilized, as the concrete would likely be exposed to water. GSI does not
practice in the field of corrosion engineering. Thus, the project architect and
structural engineer should evaluate the level of corrosion protection required for the
project and seek consultation from a qualified corrosion engineer, as warranted.
•Groundwater was encountered only in Boring B-1 at a depth of about 21½ feet. The
piezometric surface associated with perched groundwater has been as high as
10 feet below original grade, on the northern margin of the property. Perched
groundwater may be encountered during site earthwork, in excavations for deep
utilities, and may not be precluded in shallow excavations. This should be
considered in project planning and construction.
•Our evaluation indicates there are no known active faults crossing the site and the
site has very low susceptibility to deep-seated landslides; however, the hills
descending from the south on the western parcel have been mapped as having a
moderate to high potential for mud flows, which will need to be considered during
design. The potential for the site to be adversely affected by liquefaction/lateral
spreading is considered low, provided the geotechnical recommendations,
presented herein, are properly incorporated into the project design and
construction. Site soils are considered erosive. Thus, properly designed and
maintained site drainage is considered necessary from a geotechnical standpoint
to reduce damage to the planned improvements from erosion.
•The seismic acceleration values and design parameters provided herein should be
considered during the design of the proposed development. The adverse effects
of seismic shaking on the structure(s) will likely be wall cracks, some
foundation/slab distress, and some seismic settlement. However, it is anticipated
that the proposed structures will be repairable in the event of the design seismic
event. This potential should be disclosed to all interested/affected parties.
•Additional adverse geologic features that would preclude project feasibility were not
encountered, based on the available data.
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•The recommendations presented in this report should be incorporated into the
design and construction considerations of the project.
The opportunity to be of service is sincerely appreciated. If you should have any
questions, please do not hesitate to contact our office.
Respectfully submitted,
GeoSoils, Inc.
John P. Franklin David W. Skelly
Engineering Geologist, CEG 1340 Civil Engineer, RCE 47857
ATS/JPF/DWS/jh
Distribution:(3) Addressee
GeoSoils, Inc.
TABLE OF CONTENTS
SCOPE OF SERVICES ...................................................1
SITE DESCRIPTION AND PROPOSED DEVELOPMENT .........................1
FIELD STUDIES .........................................................3
REGIONAL GEOLOGY ...................................................4
SITE GEOLOGIC UNITS ..................................................6
Artificial Fill - Undocumented (Map Symbol - Afu)........................6
Artificial Fill - Roadway (Map Symbol - Afr)..............................6
Quaternary Alluvium (Map Symbol - Qal)...............................7
Tertiary Santiago Formation (Map Symbol - Tsa).........................7
GEOLOGIC STRUCTURE .................................................7
GROUNDWATER ........................................................7
ROCK HARDNESS/EXCAVATION DIFFICULTY ................................8
GEOLOGIC HAZARDS EVALUATION........................................8
Mass Wasting/Landslide Susceptibility .................................8
FAULTING AND REGIONAL SEISMICITY.....................................9
Regional Faults....................................................9
Local Faulting .....................................................9
Surface Rupture ...................................................9
Seismicity ........................................................9
Seismic Shaking Parameters ........................................10
SECONDARY SEISMIC HAZARDS .........................................11
Liquefaction/Lateral Spreading ......................................11
Seismic Densification ..............................................12
Other Geologic/Secondary Seismic Hazards ...........................12
LABORATORY TESTING .................................................13
Classification.....................................................13
Moisture-Density Relations .........................................13
Laboratory Standard...............................................13
Expansion Index..................................................14
Atterberg Limits...................................................14
Grain Size Distribution .............................................14
Direct Shear Test .................................................14
Consolidation Test ................................................15
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Saturated Resistivity, pH, and Soluble Sulfates, and Chlorides .............15
Corrosion Summary .........................................15
PRELIMINARY SETTLEMENT EVALUATION .................................16
Post-Grading Settlement ...........................................16
Seismic Settlement of Fill...........................................16
Foundation Settlement Due to Structural Loads .........................17
Settlement Summary ..............................................17
PRELIMINARY CONCLUSIONS AND RECOMMENDATIONS ....................17
GENERAL RECOMMENDATIONS .........................................20
Alternative “A”....................................................20
Advantages ................................................20
Disadvantages..............................................21
Alternative “B”....................................................21
Advantages ................................................21
Disadvantages..............................................22
EARTHWORK CONSTRUCTION RECOMMENDATIONS - ALTERNATIVE “A”.......22
General .........................................................22
Site Preparation ..................................................23
Removal and Recompaction of Potentially Compressible Earth Materials ....23
Earthwork Mitigation of Detrimentally Expansive Soils ....................23
Alternating Slot Excavations ........................................24
Perimeter Conditions ..............................................24
Fill Placement ....................................................24
Overexcavation ...................................................24
Subdrains .......................................................25
Earthwork Balance (Shrinkage/Bulking)...............................25
Import Soils......................................................25
Slope Considerations and Slope Design ..............................26
Temporary Slopes ................................................26
Excavation Observation and Monitoring (All Excavations).................26
Observation ................................................27
PRELIMINARY FOUNDATION RECOMMENDATIONS - ALTERNATIVE A ..........27
General .........................................................27
General Foundation Design.........................................28
Preliminary Foundation and Fill Settlements - Alternative A ................29
Preliminary Conventional Foundation and Slab-On-Grade Construction
Recommendations - Non Detrimentally Expansive Soils .............30
Post-Tensioned Slab Foundation Systems .............................31
Slab Subgrade Pre-Soaking ...................................32
Perimeter Cut-Off Walls.......................................33
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Post-Tensioned Foundation Design .............................33
Soil Support Parameters ......................................33
Preliminary Foundation Design and Construction Recommendations for Mat-Type
Foundations - Alternative A....................................34
Mat Foundation Design.......................................34
Slab Subgrade Moisture Content ...............................35
DRILLED PIER AND GRADE BEAM
FOUNDATION RECOMMENDATIONS (ALTERNATIVE B).................35
Passive Resistance................................................36
Point of Fixity ....................................................36
Allowable Axial Capacity ...........................................36
Caisson Construction..............................................36
Drilled Pier and Grade Beam Foundation Settlement .....................37
Corrosion and Concrete Mix ........................................37
SOIL MOISTURE TRANSMISSION CONSIDERATIONS (BOTH ALTERNATIVES)....37
WALL DESIGN PARAMETERS ............................................40
General .........................................................40
Conventional Retaining Walls .......................................40
Preliminary Retaining Wall Foundation Design ....................40
Restrained Walls ............................................41
Cantilevered Walls...........................................41
Seismic Surcharge ................................................42
Retaining Wall Backfill and Drainage..................................43
Wall/Retaining Wall Footing Transitions ...............................43
TEMPORARY SHORING DESIGN AND CONSTRUCTION ......................47
Shoring of Excavations.............................................47
Lateral Pressure - Temporary Shoring.................................48
Temporary Shoring Construction Recommendations ....................50
Monitoring of Shoring..............................................51
Monitoring of Existing Improvements ............................52
WALLS/FENCES/IMPROVEMENTS ........................................53
Perimeter Walls/Fences ............................................53
DRIVEWAY, FLATWORK, AND OTHER IMPROVEMENTS .......................53
PRELIMINARY PAVEMENT DESIGN/CONSTRUCTION ........................56
Structural Section .................................................56
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PAVEMENT GRADING RECOMMENDATIONS ...............................57
General .........................................................57
Subgrade .......................................................57
Aggregate Base ..................................................57
Paving ..........................................................58
Drainage ........................................................58
PCC Cross Gutters ................................................58
Additional Considerations ..........................................59
ONSITE INFILTRATION-RUNOFF RETENTION SYSTEMS ......................59
General .........................................................59
DEVELOPMENT CRITERIA ...............................................63
Drainage ........................................................63
Erosion Control...................................................64
Landscape Maintenance ...........................................64
Gutters and Downspouts ...........................................64
Subsurface and Surface Water ......................................64
Site Improvements ................................................65
Tile Flooring .....................................................65
Additional Grading ................................................65
Footing Trench Excavation .........................................65
Trenching/Temporary Construction Backcuts ..........................66
Utility Trench Backfill ..............................................66
SUMMARY OF RECOMMENDATIONS REGARDING GEOTECHNICAL OBSERVATION AND
TESTING........................................................67
OTHER DESIGN PROFESSIONALS/CONSULTANTS ..........................67
PLAN REVIEW .........................................................68
LIMITATIONS ..........................................................69
FIGURES:
Figure 1 - Site Location Map .........................................2
Figure 2 - Test Pit Location Map ......................................4
Detail 1 - Typical Retaining Wall Backfill and Drainage Detail ..............44
Detail 2 - Retaining Wall Backfill and Subdrain Detail Geotextile Drain .......45
Detail 3 - Retaining Wall and Subdrain Detail Clean Sand Backfill ...........46
Figure 3 - Lateral Earth Pressures for Temporary Shoring .................49
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ATTACHMENTS:
Appendix A - References ...................................Rear of Text
Appendix B - Test Pit Logs..................................Rear of Text
Appendix C - Seismicity ....................................Rear of Text
Appendix D - Laboratory Data ...............................Rear of Text
Appendix E - General Earthwork, Grading Guidelines, and Preliminary Criteria ..
..................................................Rear of Text
GeoSoils, Inc.
PRELIMINARY GEOTECHNICAL EVALUATION
9.2 ACRES, APN 212-040-56-00
LAUREL TREE LANE AT AVIARA PARKWAY
CARLSBAD, SAN DIEGO COUNTY, CALIFORNIA
SCOPE OF SERVICES
The scope of our services has included the following:
1.Review of readily available published literature, aerial photographs, and maps of the
site vicinity, including in-house nearby geotechnical reports (see Appendix A).
2.Site reconnaissance mapping and sub-surface exploration using a hollow stem
auger drill rig and cone penetrometer test soundings (CPT). Two (2) auger borings
were drilled on the east and west parcels, to a depth of approximately 50 feet.
Four (4) CPT explorations were conducted, although several more soundings were
attempted, but were not successful (refusal). Accordingly, the CPT soundings are
not in sequential order. Shear wave velocity and pore water pressure were
measured in the CPTs. All exploratory borings were backfilled per DEH guidelines
(see Appendix B).
3.In addition, and concurrently, two (2) shallow supplemental borings were advanced
for the purposes of infiltration testing in the soil type designated as “Hydrologic
Group A,” by the USDA.
4.General areal geologic and seismic hazards evaluation (see Appendix C).
5.Appropriate laboratory testing of representative undisturbed and bulk soil samples
collected during our subsurface exploration program (see Appendix D).
6.Analysis of field and laboratory data relative to the proposed development.
7.Perform an evaluation of soil settlement and liquefaction potential (Appendix E).
8.Infiltration data and City of Carlsbad Form I-8 are included in Appendix F.
9.Appropriate engineering and geologic analyses of data collected, and the
preparation of this summary report and accompaniments.
SITE DESCRIPTION AND PROPOSED DEVELOPMENT
The subject site consists of two parcels located on the east and west sides of Aviara
Parkway in the City of Carlsbad, San Diego County, California (see Figure 1, Site Location
Map). Roadway/driveway fill associated with Aviara Parkway transects the eastern third of
the site in a roughly north-south direction, descending to the west and east, separating the
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Laurel Tree Lane, Carlsbad July 7, 2016
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two parcels. Roadway fill associated with Laurel Tree Lane descends to the eastern parcel,
from the south. The Laurel Tree Lane roadway fill ranges up to about 16 feet in overall
height. The eastern portion of the site is bounded by Aviara Parkway to the west, Laurel
Tree Lane to the south and east, and a natural channel leading to a vacant lot to the north.
According to the topographic survey prepared by REC Consultants, Inc. ([REC] 2016), site
elevations range between approximately 94 and 111 feet (datum is not labeled), for an
overall relief of about 17 feet. The eastern site slopes to the northwest at a very gentle
gradient. Low hanging power lines cross on the eastern margin of this parcel. Access is
through a locked gate below the power lines on the east. The east site is vegetated with
what appears to be native weeds and plants, with a few trees along Aviara Parkway and
Laurel Tree Lane.
The western portion of the site is bounded by Aviara Parkway to the east and vacant areas
of vegetation on the remaining sides. Slopes exist on the east, south, and west sides, and
the aforementioned drainage borders the northern margin of this site. A commercial
building distributing wholesale flowers occupies the central-southerly portion of the
western site. Roadway fill associated with Aviara Parkway and two driveways ranges up
to about 23 feet in overall height. Site elevations range between a high of about 144 feet
in the southeast corner on a hillside, to a low of about 82 feet in the east-west flowing
drainage area at the northeast margin of the western property (REC, 2016), for an overall
relief of ±62 feet. The commercial site is generally flat graded, with drainage directed to
a drainage channel along the toe of the hillside to the west and southwest. The natural
portion of the west site is sparsely to moderately covered by native weeds, grasses and
shrubs, and the slopes and areas adjoining Aviara Parkway have been vegetated with
shrubs and a few trees, including palm trees. The northern and western margins are lightly
covered with grasses and weeds, with shrubs becoming more prolific to the north.
Based on our review of the preliminary architectural plans prepared by KTGY Architecture
+ Planning ([KTGY], 2016), GSI understands that proposed development includes razing
the existing building and improvements, and preparing the site to receive a new two- to
four-story multi-family residential complex with associated parking either on grade
surrounding the buildings, or in a centrally located four-story parking structure.
KTGY (2016) illustrations are preliminary and do not have any additional design information
at this time.
FIELD STUDIES
Site-specific field studies were conducted by GSI on June 15, 16, and 17, 2016, and
consisted of reconnaissance geologic mapping, and excavating two (2) hollow-stem auger
borings, one on each parcel, followed by four (4) CPT soundings (two on each parcel).
Additional, two (2) shallow borings were advanced for infiltration purposes, one on each
parcel. The borings were logged by a representative of this office who collected relatively
undisturbed and representative bulk soil samples for appropriate laboratory testing. The
logs of the explorations are presented in Appendix B. Site geology and the location of the
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borings and CPT soundings are presented on the Boring Location Map (see Figure 2),
which uses REC (2016) as a base.
REGIONAL GEOLOGY
The site is located near the boundary between the coastal plain and the central mountain-
valley physiographic sections of San Diego County. The coastal plain section is
characterized by pronounced marine wave-cut terraces intermittently dissected by stream
channels that convey water from the eastern highlands to the Pacific Ocean. The central
mountain-valley section is characterized by ridges and intermontane basins. The basins
or valleys range between 500 and 5,000 feet in elevation and are likely due to multiple
erosion cycles. However, several of the larger intermontane basins owe their configuration
to structural control and erosion of crystalline rocks. Mountain peaks in this physiographic
section ascend to elevations greater than 6,000 feet.
San Diego County lies within the Peninsular Ranges Geomorphic Province of southern
California. This province is characterized as elongated mountain ranges and valleys that
trend northwesterly (Norris and Webb, 1990). This geomorphic province extends from the
base of the east-west aligned Santa Monica - San Gabriel Mountains, and continues south
into Baja California, Mexico. The mountain ranges within this province are underlain by
basement rocks consisting of pre-Cretaceous metasedimentary rocks, Jurassic
metavolcanic rocks, and Cretaceous plutonic (granitic) rocks.
The San Diego County region was originally a broad area composed of pre-batholithic
rocks that were subsequently subjected to tectonism and metamorphism. In the late
Cretaceous Period, the southern California Batholith was emplaced causing the
aforementioned metamorphism of pre-batholithic rocks. Many separate magmatic
injections originating from this body occurred along zones of structural weakness.
Following batholith emplacement, uplift occurred, resulting in the removal of the overlying
rocks by erosion. Erosion continued until the area was that of low relief and highly
weathered. The eroded materials were deposited along the sea margins. Sedimentation
also occurred during the late Cretaceous Period. However, subsequent erosion has
removed much of this evidence. In the early Tertiary Period, terrestrial sedimentation
occurred on a low-relief land surface. In Eocene time, previously fluctuating sea levels
stabilized and marine deposition occurred. In the late Eocene, regional uplift produced
erosion and thick deposition of terrestrial sediments. In the middle Miocene, the
submergence of the Los Angeles Basin resulted in the deposition of thick marine beds in
the northwestern portion of San Diego County. During the Pliocene, marine sedimentation
was more discontinuous and generally occurred within shallow marine embayments. The
Pleistocene saw regressive and transgressive sea levels that fluctuated with prograding
and recessive glaciation. The changes in sea level had a significant effect on coastal
topography and resultant wave erosion and deposition formed many terraces along the
coastal plain. In the mid-Pleistocene, regional faulting separated highland erosional
surfaces into major blocks lying at varying elevations. A later rise in sea level, during the
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late Pleistocene caused the deposition of thick alluvial deposits within the coastal river
channels. In recent geologic time, crystalline rocks have weathered to form residuum,
highland areas have eroded, and deposition of river, lake, and beach sediments has
occurred.
Regional geologic mapping by Kennedy and Tan (2005 and 2007) shows the site is
underlain by late Holocene unconsolidated alluvial flood plain deposits. Kennedy and Tan
(2005 and 2007) suggest that these site deposits are underlain by middle Eocene
sedimentary bedrock belonging to the Santiago Formation. However, the surface and
subsurface data acquired during our site-specific field investigation indicated somewhat
differing geologic conditions, as discussed below.
SITE GEOLOGIC UNITS
The site geologic units encountered or observed during our subsurface exploration and
site reconnaissance include roadway fill, undocumented artificial fill, Holocene
unconsolidated alluvial flood plain deposits, and sedimentary bedrock belonging to the
Tertiary Santiago Formation. The earth materials are generally described, below, from the
youngest to the oldest. The distribution of these materials is shown on Figure 2.
Artificial Fill - Undocumented (Map Symbol - Afu)
Undocumented artificial fill was observed mantling the site in Borings B-1, B-2, CPT-1,
CPT-2, CPT-4A, and CPT-6. As observed, the fill was generally comprised of reddish
yellow to light brown, to yellow brown, to light gray, sandy clays to sandy silts, with local
gravels and asphalt debris. The fill was dry to moist, and loose to medium stiff. The fill was
observed to extend to depths on the order of 3 to perhaps ±7 feet below the existing
grades (b.e.g.), on the western parcel, and about 10 to 13 feet thick on the eastern parcel.
Owing to the lack of documentation regarding engineering suitability and the observed
non-uniformity, the existing fill is considered potentially compressible in its existing state.
Mitigation of the existing fill is recommended, should settlement-sensitive improvements
or additional fill be proposed within its influence.
Artificial Fill - Roadway (Map Symbol - Afr)
Although not encountered in our borings, roadway fill is associated with the embankments
ascending to Aviara Parkway on both parcels, and Laurel Tree Lane on the eastern parcel.
Roadway fill associated with Aviara Parkway and the two driveways on the western parcel
ranges up to about 23 feet thick, or more. The Laurel Tree Lane roadway fill ranges up to
about 16 feet thick, or more. Similar to the undocumented fill, the existing fill is considered
potentially compressible in its existing state. Mitigation of the existing fill is recommended,
should settlement-sensitive improvements or additional fill be proposed within its influence.
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Quaternary Alluvium (Map Symbol - Qal)
Holocene unconsolidated alluvial flood plain deposits were encountered at shallow depth
on the easterly parcel, underlying the undocumented fill. As observed, the alluvium
extended to depths on the order of 9 to 13 feet below the undocumented fill. The alluvium
typically consisted of dark reddish brown, fine-grained sandy clay, with traces of pebbles.
The alluvium was generally damp and loose. The alluvial deposits are considered
potentially compressible in their existing state. As such, they should not be used for the
support of settlement-sensitive improvements and/or new planned fills without mitigation.
Tertiary Santiago Formation (Map Symbol - Tsa)
The site is underlain at the surface and shallow depth by the middle Eocene-age
Santiago Formation. In general, the weathered portions of the Santiago Formation
consisted of dark reddish brown, silty sandstone, that was moist and dense. Unweathered
Santiago Formation was encountered at approximate depths of 0 to 6½ feet below the
weathered portion. As observed, the unweathered Santiago Formation consisted of
varying shades of light gray and yellowish brown silty sandstone, and light yellow brown
to yellowish gray claystone. Unweathered Santiago Formation was generally very moist
to wet to saturated, and medium dense/medium stiff-stiff to very dense.
GEOLOGIC STRUCTURE
The alluvium is typicallythickly bedded and is gently inclined in a southwesterly direction,
mimicking areal topography. Kennedy and Tan (2005 and 2007) show that
Santiago Formation bedding in the site vicinity is inclined about 10 degrees to the
southwest.
GROUNDWATER
Groundwater was encountered only in Boring B-1 at a depth of about 21½ feet. Thus, it
appears that perched groundwater forms a piezometric surface, at least on the east site.
The piezometric surface associated with perched groundwater has been as high as 10 feet
below original grade, on the northern margin of the property (Robert Prater Associates,
1997). Based on a review of in-house, proprietary data, the regional groundwater table is
estimated to be nearly coincident with sea level, or deeper than 50 feet. However, the
elevation of the groundwater table may vary depending on the time of year and
precipitation.
Perched groundwater conditions along zones of contrasting permeabilities and/or densities
(i.e., fill/alluvium contacts, younger and sandy/clayey fill lifts, bedrock discontinuities, etc.)
may not be precluded from occurring in the future due to site irrigation, increased
precipitation, poor drainage conditions, or damaged underground utilities, and should be
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anticipated. Should perched groundwater conditions develop after development, this
office could assess the affected area(s) and provide the appropriate recommendations to
mitigate the observed groundwater conditions
Due to the potential for shallow perched water conditions, more onerous slab design is
necessary for any new slab-on-grade floor (State of California, 2016). Recommendations
for reducing the amount of water and/or water vapor through slab-on-grade floors are
provided in the “Soil Moisture Considerations” sections of this report.
ROCK HARDNESS/EXCAVATION DIFFICULTY
Excavations with standard mechanized earth-moving equipment are anticipated to be
relatively easy with respect to difficulty. However, localized areas of highly cemented
Santiago Formation could present very difficult excavation, if encountered. Excavation
equipment should be appropriately suited for the required excavation task. Excavations
deeper than about 10 feet have an elevated potential to encounter groundwater and/or
saturated soils, which could hinder job progress.
GEOLOGIC HAZARDS EVALUATION
Mass Wasting/Landslide Susceptibility
Mass wasting refers to the various processes by which earth materials are moved down
slope in response to the force of gravity. Examples of these processes include slope
creep, surficial failures, and deep-seated landslides. Creep is the slowest form of mass
wasting and generally involves the outer 5 to 10 feet of a slope surface. During heavy
rains, such as those in El Niño years, creep-affected materials may become saturated,
resulting in a more rapid form of downslope movement (i.e., landslides and/or surficial
failures).
Geomorphic expressions indicative of past significant mass wasting events (i.e., scarps
and hummocky terrain) were not observed during our field studies. Further, no adverse
geologic structures were encountered during our subsurface exploration nor during our
review of regional geologic maps. The City of Carlsbad (1992) indicates that the hills to the
south of the western parcel have a moderate to high mud flow potential.
The onsite soils are, however, considered highly erosive. Therefore, the project should
include prudent surface drainage controls that direct water away from foundations and
tops of slopes (if slopes are planned).
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FAULTING AND REGIONAL SEISMICITY
Regional Faults
Our review indicates that there are no known active faults crossing the project area
and the site is not within an Alquist-Priolo Earthquake Fault Zone (Bryant and Hart, 2007).
However, the site is situated in a region subject to periodic earthquakes along active faults.
The Rose Canyon fault is the closest known active fault to the site (located at a distance
of approximately 5.3 miles [8.6 kilometers]) and should have the greatest effect on the site
in the form of strong ground shaking, should the design earthquake occur. According to
Cao, et al. (2003), the Rose Canyon fault has a slip rate of 1.5 (±0.5) millimeters per year;
and therefore, is classified as a “B” fault. Cao, et al. (2003) further indicate that the
Rose Canyon fault is capable of a maximum magnitude 7.2 earthquake. The location of
the Rose Canyon fault and other major faults relative to the site are shown on the
“California Fault Map” in Appendix C. The possibility of ground acceleration, or shaking
at the site, may be considered as approximately similar to the southern California region
as a whole.
Local Faulting
According to Kennedy and Tan (2005 and 2007), no known active faults specifically
transect the subject site. An old faults transects the easterly parcel, trending north-south,
occurs in the Santiago Formation, and is generally coincident with that portion of
Laurel Tree Lane that also trends north-south. These faults are not considered active
(Bryant and Hart, 2007).
Surface Rupture
Owing to the lack of known active faults crossing the site, the potential for the proposed
development to be adversely affected by surface rupture from fault movement is
considered very low.
Seismicity
The acceleration-attenuation relation of Bozorgnia, Campbell, and Niazi (1999) has been
incorporated into EQFAULT (Blake, 2000a). EQFAULT is a computer program developed
by Thomas F. Blake (2000a), which performs deterministic seismic hazard analyses using
digitized California faults as earthquake sources.
The program estimates the closest distance between each fault and a given site. If a fault
is found to be within a user-selected radius, the program estimates peak horizontal ground
acceleration that may occur at the site from an upper bound (formerly “maximum credible
earthquake”), on that fault. Upper bound refers to the maximum expected ground
acceleration produced from a given fault. Based on the EQFAULT program, a peak
horizontal ground acceleration from an upper bound event on the Rose Canyon fault may
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be on the order of 0.55g. The computer printouts of pertinent portions of the EQFAULT
program are included within Appendix C.
Historical site seismicity was evaluated with the acceleration-attenuation relation of
Bozorgnia, Campbell, and Niazi (1999), and the computer program EQSEARCH
(Blake, 2000b, updated to January 2015). This program performs a search of the historical
earthquake records for magnitude 5.0 to 9.0 seismic events within a 100-kilometer radius,
between the years 1800 through January 2015. Based on the selected
acceleration-attenuation relationship, a peak horizontal ground acceleration is estimated,
which may have affected the site during the specific event listed. Based on the available
data and the attenuation relationship used, the estimated maximum (peak) site
acceleration during the period 1800 through January 2015 was about 0.31 g. A historic
earthquake epicenter map and a seismic recurrence curve are also estimated/generated
from the historical data. Computer printouts of the EQSEARCH program are presented in
Appendix C.
Seismic Shaking Parameters
Based on the site conditions, the following table summarizes the site-specific design
criteria obtained from the 2013 CBC (CBSC, 2013), Chapter 16 Structural Design,
Section 1613, Earthquake Loads. The computer program “U.S. Seismic Design Maps,
provided by the United States Geological Survey (http://geohazards.usgs.gov/
designmaps/us/application.php) was utilized for design. The short spectral response
utilizes a period of 0.2 seconds.
2013 CBC SEISMIC DESIGN PARAMETERS
PARAMETER VALUE 2013 CBC AND/OR REFERENCE
Site Class D Section 1613.3.2/ASCE 7-10
(Chapter 20)
sSpectral Response - (0.2 sec), S 1.105 g Figure 1613.3.1(1)
1Spectral Response - (1 sec), S 0.425 g Figure 1613.3.1(2)
aSite Coefficient, F 1.058 Table 1613.3.3(1)
vSite Coefficient, F 1.575 Table1613.3.3(2)
Maximum Considered Earthquake Spectral
MSResponse Acceleration (0.2 sec), S 1.169 g Section 1613.3.3
(Eqn 16-37)
Maximum Considered Earthquake Spectral
M1Response Acceleration (1 sec), S 0.670 g Section 1613.3.3
(Eqn 16-38)
5% Damped Design Spectral Response
DSAcceleration (0.2 sec), S 0.779 g Section 1613.3.4
(Eqn 16-39)
5% Damped Design Spectral Response
D1Acceleration (1 sec), S 0.446 g Section 1613.3.4
(Eqn 16-40)
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Seismic Design Category D Section 1613.3.5/ASCE 7-10
(Table 11.6-1 or 11.6-2)
MPGA 0.464 g ASCE 7-10 (Eqn 11.8.1)
GENERAL SEISMIC PARAMETERS
Distance to Seismic Source - (Rose Canyon fault)5.3 mi (8.6 km)(1)
WUpper Bound Earthquake (Rose Canyon fault)M = 7.2(2)
- From Blake (2000a)(1)
- Cao, et al. (2003)(2)
Conformance to the criteria above for seismic design does not constitute any kind of
guarantee or assurance that significant structural damage or ground failure will not occur
in the event of a large earthquake. The primary goal of seismic design is to protect life, not
to eliminate all damage, since such design may be economically prohibitive. Cumulative
effects of seismic events are not addressed in the 2013 CBC (CBSC, 2013) and regular
wmaintenance and repair following locally significant seismic events (i.e., M 5.5) will likely
be necessary, as is the case in all of southern California.
SECONDARY SEISMIC HAZARDS
Liquefaction/Lateral Spreading
Liquefaction describes a phenomenon in which cyclic stresses, produced by
earthquake-induced ground motion, create excess pore pressures in relatively
cohesionless soils. These soils may thereby acquire a high degree of mobility, which can
lead to vertical deformation, lateral movement, lurching, sliding, and as a result of seismic
loading, volumetric strain and manifestation in surface settlement of loose sediments, sand
boils and other damaging lateral deformations. This phenomenon occurs only below the
water table, but after liquefaction has developed, it can propagate upward into overlying
non-saturated soil as excess pore water dissipates.
One of the primary factors controlling the potential for liquefaction is depth to groundwater.
Typically, liquefaction has a relatively low potential at depths greater than 50 feet and is
unlikely and/or will produce vertical strains well below 1 percent for depths below 60 feet
when relative densities are 40 to 60 percent and effective overburden pressures are two
or more atmospheres (i.e., 4,232 pounds per square foot [Seed, 2005]).
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The condition of liquefaction has two principal effects. One is the consolidation of loose
sediments with resultant settlement of the ground surface. The other effect is lateral
sliding. Significant permanent lateral movement generally occurs only when there is
significant differential loading, such as fill or natural ground slopes within susceptible
materials. These conditions do not exist at the site.
Liquefaction susceptibility is related to numerous factors and the following five conditions
should be concurrently present for liquefaction to occur: 1) sediments must be relatively
young in age and not have developed a large amount of cementation; 2) sediments must
generally consist of medium- to fine-grained, relatively cohesionless sands; 3) the
sediments must have low relative density; 4) free groundwater must be present in the
sediment; and 5) the site must experience a seismic event of a sufficient duration and
magnitude, to induce straining of soil particles. Effects of liquefaction may include sand
boils, settlement, and bearing capacity failures.
Based on our review of in-house, proprietary data and our recent findings, the subject site
has a low susceptibility to damaging deformations resulting from seismic-induced
liquefaction, provided the recommendations in this report are incorporated into project
design and construction. This assessment considers the consolidated, fine-grained nature
of the Santiago Formation, which underlies the site at a relatively shallow depth.
Seismic Densification
Seismic densification is a phenomenon that typically occurs in low relative density granular
soils (i.e., United States Soil Classification System [USCS] soil types SP, SW, SM, and SC)
that are above the groundwater table. These unsaturated granular soils are susceptible
if left in the original density (unmitigated), and are generally dry of the optimum moisture
content (as defined by the ASTM D 1557). During seismic-induced ground shaking, these
natural or artificial soils deform under loading and volumetrically strain, potentially resulting
in ground surface settlements. Provided that the earthwork and foundation
recommendations contained in this report are implemented during project planning and
construction, the potential for seismic densification to adversely affect the proposed
development is considered low. However, some densification of the adjoining un-mitigated
properties may influence improvements at the perimeter of the site and proposed
improvements not supported by deep foundations or recompacted engineered fill may be
susceptible to seismic densificaiton. Special setbacks and/or deepened foundations may
be utilized if significant structures/improvements are placed close to the perimeter of the
site. Our evaluation assumed that the current offsite conditions will not be significantly
modified by future grading at the time of the design earthquake, which is a reasonably
conservative assumption.
Other Geologic/Secondary Seismic Hazards
The following list includes other geologic/seismic related hazards that have been
considered during our evaluation of the site. The hazards listed are considered negligible
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and/or mitigated as a result of site location, soil characteristics, and typical site
development procedures:
•Subsidence
•Ground Lurching or Shallow Ground Rupture
•Seiche
•Tsunami
LABORATORY TESTING
Laboratory tests were performed on representative bulk and relatively undisturbed
samples of site earth materials collected during our subsurface exploration in order to
evaluate their physical characteristics. Test procedures used and results obtained are
presented below.
Classification
Soils were classified visually according to the Unified Soils Classification System, in
general accordance with ASTM D 2487 and D 2488. The soil classifications are shown on
the Boring Logs and CPT soundings in Appendix B.
Moisture-Density Relations
The field moisture contents and dry unit weights were determined for relatively undisturbed
samples of site earth materials in the laboratory. Testing was performed in general
accordance with ASTM D 2937 and ASTM D 2216. The dry unit weight was determined
in pounds per cubic foot (pcf), and the field moisture content was determined as a
percentage of the dry weight. The results of these tests are shown on the Boring Logs in
Appendix B.
Laboratory Standard
The maximum density and optimum moisture content was evaluated for the major soil type
encountered in the borings. The laboratory standard used was ASTM D-1557. The
moisture-density relationships obtained for these soils are shown on the following table:
SAMPLE LOCATION
AND DEPTH (FT)SOIL TYPE MAXIMUM DENSITY
(PCF)
OPTIMUM MOISTURE
CONTENT (%)
B-1 @ 3-7 Brown, Silty SAND 123.0 11.5
B-2 @ 5 Grey, Sandy CLAY 122.0 13.0
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Expansion Index
A representative sample of near-surface site soils was evaluated for expansion potential.
Expansion Index (E.I.) testing and expansion potential classification was performed in
general accordance with ASTM Standard D 4829, the results of the expansion testing are
presented in the following table.
SAMPLE LOCATION
AND DEPTH (FT)EXPANSION INDEX EXPANSION POTENTIAL
B-1 @ 15 32 Low
B-2 @ 5 72 Medium
Atterberg Limits
Testing was performed on a representative fine-grained soil sample to evaluate the liquid
limit, plastic limit, and plasticity index (P.I.) in general accordance with ASTM D-4318. The
test results are presented below:
SAMPLE LOCATION
AND DEPTH (FT)LIQUID LIMIT PLASTIC LIMIT PLASTICITY INDEX
B-2 @ 5 45 16 29
Grain Size Distribution
An evaluation was performed on a selected representative soil sample in general
accordance with ASTM D 422. The grain-size distribution curve is presented in
Appendix D.
Direct Shear Test
Shear testing was performed on a representative bulk sample of site soil in general
accordance with ASTM test method D 3080 in a Direct Shear Machine of the strain control
type. Prior to testing, the sample was remolded to 90 percent of the laboratory standard
(ASTM D 1557). The shear test results are presented as follows:
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LOCATION AND
DEPTH (FT)
PRIMARY RESIDUAL
COHESION
(PSF)
FRICTION ANGLE
(DEGREES)
COHESION
(PSF)
FRICTION ANGLE
(DEGREES)
B-1 @ 5
(Undisturbed)267 32 310 32
B-2 @ 5
(Remolded)359 29 304 29
Consolidation Test
Consolidation testing was performed on a selected, relatively undisturbed sample of the
onsite soils. Testing was performed in general accordance with ASTM Test Method
D 2435. Test results are presented in Appendix D.
Saturated Resistivity, pH, and Soluble Sulfates, and Chlorides
GSI conducted sampling of onsite earth materials for general soil corrosivity and soluble
sulfates, and chlorides testing. The testing included evaluation of soil pH, soluble sulfates,
chlorides, and saturated resistivity. Test results are presented in the following table:
SAMPLE LOCATION
AND DEPTH (FT)pH
SATURATED
RESISTIVITY
(ohm-cm)
SOLUBLE
SULFATES
(% by weight)
SOLUBLE
CHLORIDES
(ppm)
B-1 @3-7 6.43 350 0.0375 40
B-2 @ 5 5.53 240 0.0195 35
Corrosion Summary
Laboratory testing indicates that tested samples of the onsite soils are: medium acid to
slightly acid with respect to soil acidity/alkalinity; severely corrosive to exposed, buried
metals when saturated; present a negligible (“not applicable” per American Concrete
Institute [ACI] 318-11) sulfate exposure to concrete; and have low to slightly elevated
concentrations of soluble chlorides. GSI does not practice in the field of corrosion
engineering. Thus, the project architect and structural engineer should evaluate the level
of corrosion protection required for the project and seek consultation from a qualified
corrosion engineer, as warranted.
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PRELIMINARY SETTLEMENT EVALUATION
GSI has estimated the potential total vertical settlement, differential settlement for the site.
The analyses were based on laboratory test results and subsurface data collected from
borings and CPT data completed in preparation of this study. Site specific conditions
affecting settlement potential include the areal depositional environment, grain size and
lithology of sediments, cementing agents, stress history, moisture history, material shape,
density, void ratio, etc. Ground settlement should be anticipated due to primary
consolidation and secondary compression of engineered fill and potential left-in-place
alluvium, and weathered and unweathered Santiago Formation under new foundation and
fill loads. The amount of total vertical settlement, and time over which it occurs, is
dependent upon various factors, including material type, depth of fill, depth of removals,
initial and final moisture content (groundwater elevation), and in-place density of
subsurface materials and new foundation loads. For the proposed buildings, GSI
anticipates that wall loads will be on the order of 5 to 8 kips, and column loads will range
between approximately 20 to 200 kips.
Post-Grading Settlement
Site grading is anticipated to consist of maximum planned cuts and fills on the order of 3
feet from existing grades. In planned fill areas remedial grading may add an additional 5
to 17 feet of compacted fill. Thus, the maximum thickness of engineered fill is anticipated
to be 20 feet, on a preliminary basis. As such, the magnitude of this settlement is
considered to be relatively low, with total vertical static settlements of approximately ¾ to
2 inches anticipated after grading is complete. Total fill settlement may be revised,
dependant on conditions exposed during grading and review of final foundation and
grading plans. Monitoring following grading should be performed to evaluate expansion
characteristics of the exposed subsurface soils and compaction due to mitigated fill.
Seismic Settlement of Fill
The magnitude of potential seismic settlement was evaluated. Based upon the assumed
design configuration and the results of our seismic settlement analysis, the total ground
settlement, across the site, during the design basis seismic event is anticipated to be on
the order of ½ to 1 inch, with a potential differential seismic settlement of approximately ¼
to ¾ inch over 50 feet horizontally (i.e., angular distortion approximately 1/800), given
recommended mitigation and current site conditions. This minimal level of deformation
should be considered in foundation design and planning, in addition to foundation
settlement under static loading conditions. This anticipated seismic-induced settlement
may be mitigated by foundation type, grading and/or ground modification. If mitigated
soils and foundations are completed, surface manifestations during the design basis
earthquake should be limited to 1 inch total seismic settlement and differential seismic
settlement of ¾ inches over 50 feet.
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Foundation Settlement Due to Structural Loads
The settlement of the structures supported on structural concrete mats or slabs founded
on compacted fill will depend on the actual foundation dimensions, the thickness and
compressibility of fill below the bottom of the foundation, and the imposed structural loads.
GSI has assumed that the existing graded pad on the west parcel will not be altered by
more than 2 feet (i.e., new fill loads 0 to 2 feet). Provided the thickness of recompacted fill
below the bottom of the foundation is based on a maximum allowable bearing pressure,
provided in this report, post-construction total vertical static settlement of less than 1 inch
should be anticipated; however, this assumes all fill is properly compacted. Given this
condition, the majority of the foundation settlement should occur as the building loads are
applied during construction. Differential settlement between the lightest and heaviest
loading condition may occur across the foundation, and is anticipated to minimally be on
the order of ½ to 1 inch in 30 feet (about 1/350) or between the heaviest and lightest
loaded areas of the foundation. Further review will be needed once draft foundation plans
and building loads are provided.
Settlement Summary
Static differential settlement of up to 1 inch in 40 feet (1/480) in should be incorporated into
the foundation system design. Dynamic deformations (i.e., angular distortion
approximately 1/800), should be evaluated in the design as part of the seismic
performance of the building and other improvements onsite.
PRELIMINARY CONCLUSIONS AND RECOMMENDATIONS
Based on our field exploration, laboratory testing, and geotechnical engineering analysis,
it is our opinion that the subject site is suitable for the proposed residential development
from a geotechnical engineering and geologic viewpoint, provided that the
recommendations presented in the following sections are incorporated into the design and
construction phases of site development. The primary geotechnical concerns with respect
to the proposed development and improvements are:
•Earth materials characteristics and depth to competent bearing material.
•Presence of undocumented fill, should settlement-sensitive improvements be
proposed within its influence.
•Presence of potentially compressible roadway fill, should settlement-sensitive
improvements be proposed within its influence.
•Temporary slope stability and the need for alternating slot excavations or shoring
along the roadway fill, if remedial earthwork is performed.
•On-going expansion and corrosion potential of site soils, and the presence of
detrimentally expansive soils (as defined in the 2013 CBC).
•Erosiveness of site earth materials, and potential for mud flows to impact the
western parcel, emanating from the hills to the south.
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•Perimeter conditions and planned improvements near the property boundary.
•A relatively shallow groundwater table.
•Regional seismic activity and the potential for earthquake-induced ground motions
to affect the proposed development.
The recommendations presented herein consider these as well as other aspects of the site.
The engineering analyses performed concerning site preparation and the
recommendations presented herein have been completed using the information provided
and obtained during our field work.
In the event that any significant changes are made to proposed site development, the
conclusions and recommendations contained in this report shall not be considered valid
unless the changes are reviewed and the recommendations of this report verified or
modified in writing by this office. Foundation design parameters are considered
preliminary until the foundation design, layout, and structural loads are provided to this
office for review.
1.Soil engineering, observation, and testing services should be provided during
grading to aid the contractor in removing unsuitable soils and in his effort to
compact the fill.
2.Geologic observations should be performed during any grading and foundation
construction to verify and/or further evaluate geologic conditions. Although unlikely,
if adverse geologic structures are encountered, supplemental recommendations
and earthwork may be warranted.
3.Based on our review, the site is susceptible to moderate to severe ground shaking
should an earthquake occur on any of the regionally active fault systems. This will
need to be considered in the structural design of the proposed residential structure.
The primary purpose of building codes in regard to seismic design is to protect life
and safety; not to eliminate all structural damage.
4.All undocumented artificial fill, roadway fill, alluvium, and weathered bedrock are
considered unsuitable for the support of the proposed settlement-sensitive
improvements, and new planned fills. These potentially compressible earth
materials will require mitigation, as recommended herein, where they are within the
influence of the proposed settlement-sensitive improvements. Mitigation would
include removal and recompaction of unsuitable soils.
5.Expansion Index (E.I.) testing, performed on a representative sample of the site
soils, indicates low to medium, and possibly highly expansive conditions. Based
on classification index tests, site soils are considered detrimentally expansive and
warrant special foundation and slab-on-grade floor designs to resist the damaging
effects of expansive soils.
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6.Laboratory testing indicates that tested samples of the onsite soils are: medium acid
to slightly acid with respect to soil acidity/alkalinity; severely corrosive to exposed,
buried metals when saturated; present a negligible (“not applicable” per American
Concrete Institute [ACI] 318-11) sulfate exposure to concrete; and have low to
slightly elevated concentrations of soluble chlorides. GSI does not practice in the
field of corrosion engineering. Thus, the Client and project architect should agree
on the level of corrosion protection required for the project and seek consultation
from a qualified corrosion consultant as warranted. The use of concrete conforming
to Exposure Class C1 in American Concrete Institute (ACI) 318-11, should be
utilized, as the concrete would likely be exposed to water.
7.Site soils are considered erosive. Surface drainage should be designed to eliminate
the potential for concentrated flows. Positive surface drainage away from
foundations is recommended. Temporary erosion control measures should be
implemented until vegetative covering is well established. The homeowners should
maintain proper surface drainage over the life of the project.
8.Groundwater was encountered only in Boring B-1 at a depth of about 21½ feet. The
piezometric surface associated with perched groundwater has been as high as
10 feet below original grade, on the northern margin of the property. Perched
groundwater may be encountered during site earthwork, in excavations for deep
utilities, and may not be precluded in shallow excavations. This should be
considered in project planning and construction.
9.Perimeter conditions and existing offsite improvements will limit the removal and
recompaction of potentially compressible soils near the margins of the site. As
such, any settlement-sensitive improvement at the property line would require
deepened foundations, additional reinforcement, or would retain some potential for
distress and therefore, a reduced serviceable life. Alternatively, unsuitable soils
near the property lines may be removed and recompacted in alternating slot or
shored excavations.
10.On a preliminary basis, temporary slopes should be constructed in accordance with
CAL-OSHA guidelines for Type “B” soils, provided water, seepage, or other adverse
geologic conditions are not present. All temporary slopes should be evaluated by
the geotechnical consultant, prior to worker entry. Should adverse conditions be
identified, the slope may need to be laid back to a flatter gradient or require the use
of shoring. Alternating “A,” “B,” and “C” slot excavations may be used to perform
the recommended remedial earthwork near the property lines/roadway fill in lieu of
shoring.
11.The design civil engineer should consider the potential for mud flows to affect the
westerly site, emanating from the hills to the south, and provide mitigation in the
form of elevated pads, or setbacks from natural slopes, or walls with freeboard, etc.
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12.The seismicity-acceleration values provided herein should be considered during the
design and construction of the proposed development.
13.General Earthwork, Grading Guidelines, and Preliminary Criteria are provided at the
end of this report as Appendix G. Specific recommendations are provided below.
GENERAL RECOMMENDATIONS
Owing to the depth to competent bearing materials, and the proximity of offsite
improvements on adjoining properties, GSI is providing two (2) alternative geotechnical
engineering scenarios for remedial earthwork and foundation construction. These are
referred to hereinafter as Alternatives “A” and “B.” Alternative “A” includes remedial
earthwork to remove and recompact the low density, surficial undocumented fill and
roadway fill, alluvium, and weathered bedrock deposits, if settlement sensitive
improvements are proposed close to the existing roadways. Obviously, this would not be
necessary if proposed improvements are kept well away from the existing roadways and/or
property lines. Alternative “B” includes very little to no remedial grading and the use of a
drilled pier and grade beam foundation system with a structural slab-on-grade floor for the
support of the proposed residential structures on the east parcel. Possible advantages
and disadvantages of both alternatives are discussed below. GSI recommends that the
selection of the preferred alternative be based on value engineering studies that at a
minimum evaluate quality (i.e., long-term performance), speed of construction, and
construction costs.
Alternative “A”
Advantages
Possible advantages of Alternative “A” are:
•The removal and recompaction of low density surficial soils would allow for the use
of a shallow foundation system.
•Possible lower costs than a deep foundation system unless shoring is used.
•Less potential for distress to ancillary site improvements if remedial grading is
performed across the entire property.
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Disadvantages
Possible disadvantages of Alternative “A” are:
•Potential sloughing of the excavation walls at the property lines that may extend into
the adjoining properties. This may require some repair of any damaged offsite
property.
•Remedial excavations near Aviara Parkway and Laurel Tree Lane will need to be
completed in alternating slot or shored excavations.
•Will require pre-construction surveys and excavation monitoring.
•Soils too saturated to properly compact may be encountered at depth, and would
require drying back or blending with drier materials to achieve compaction.
•Heavy equipment vibrations could potentially damage offsite improvements.
•The speed of construction will likely be relatively slow as compared to
Alternative “B.”
•Foundation settlements may be greater than Alternative “B.”
Alternative “B”
Advantages
Possible advantages of Alternative “B” are:
•A smaller magnitude of foundation settlement than Alternative “A.”
•A likely faster speed of construction than Alternative “A” as a result of the little to no
remedial earthwork required.
•Increased foundation performance.
•Lower likelihood for damage to existing improvements on adjoining properties.
•Would not require as much excavation and vibration monitoring as Alternative “A.”
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Disadvantages
Possible disadvantages of Alternative “B” are:
•The possible need for casing of the drilled shafts, owing to the relatively
cohesionless nature of some of the surficial earth materials and a potential perched
groundwater table.
•The need for structural slab-on-grade floors that are capable of supporting the
applied net loading conditions without the aid of the underlying soils.
•The possible need to penetrate grade beams to install the under-slab utilities.
•Reduced performance of ancillary site improvements if remedial grading is not
performed and if the improvements are not pier-supported.
•The possible need for chloride resistant concrete and corrosion-protected
reinforcing bars in drilled pier construction.
EARTHWORK CONSTRUCTION RECOMMENDATIONS - ALTERNATIVE “A”
General
All earthwork should conform to the guidelines presented in the 2013 CBC (CBSC, 2013),
the requirements of the City of Carlsbad, and the General Earthwork and Grading
Guidelines presented in Appendix G, except where specifically superceded in the text of
this report. Prior to earthwork, a GSI representative should be present at the pre-
construction meeting to provide additional earthwork guidelines, if needed, and review the
earthwork schedule. This office should be notified in advance of any fill placement,
supplemental regrading of the site, or backfilling underground utility trenches and retaining
walls after rough earthwork has been completed. This includes grading for driveway
approaches, driveways, and exterior hardscape.
During earthwork construction, all site preparation and the general grading procedures of
the contractor should be observed and the fill selectively tested by a representative(s) of
GSI. If unusual or unexpected conditions are exposed in the field, they should be reviewed
by this office and, if warranted, modified and/or additional recommendations will be
offered. All applicable requirements of local and national construction and general industry
safety orders, the Occupational Safety and Health Act (OSHA), and the Construction Safety
Act should be met. It is the onsite general contractor’s and individual subcontractors’
responsibility to provide a safe working environment for our field staff who are onsite. GSI
does not consult in the area of safety engineering. It is also the responsibility of the
contractor to provide protection of their work product. Surface drainage should be
directed away from open excavations.
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Site Preparation
Any existing improvements, vegetation and deleterious debris should be removed from the
site, prior to the start of construction, if they are located in areas of proposed earthwork.
Any remaining cavities should be observed by the geotechnical consultant. Mitigation of
cavities would likely include removing any potentially compressible soils to expose
unweathered Santiago Formation and then backfilling the excavation with a controlled
engineered fill or soils that have been moisture conditioned to optimum moisture content
and compacted to at least 90 percent of the laboratory standard (ASTM D 1557).
Should the onsite sewage disposal/holding system be encountered during earthwork, this
office should be contacted to provide recommendations for removal and disposal.
Removal and Recompaction of Potentially Compressible Earth Materials
Potentially compressible undocumented and roadway fill, alluvium, and weathered
bedrock should be removed to expose unweathered bedrock (Santiago Formation).
Excluding roadway fill areas, based on the available subsurface data, remedial grading
excavations are anticipated to extend to depths on the order of 17 to 20 feet below existing
grades, on the east parcel, and about 3 to 7 feet below existing grade on the west parcel.
Following excavation, the exposed subsoils should be scarified at least 6 to 8 inches,
moisture conditioned to at least optimum moisture content, and then compacted to at least
90 percent of laboratory standard (ASTM D 1557). The removed soils may be reused as
engineered fill provided they are not too wet to compact, and cleaned of any vegetation
and deleterious debris prior to placement. Remedial grading excavations should extend
below a 1:1 (h:v) plane down from the perimeter of the proposed building footprint at the
bearing elevation, and should be observed by the geotechnical consultant prior to
scarification and fill placement. Alternating slot excavations, as recommended below,
should be used to complete the remedial excavations below a 1½:1 (h:v) plane down from
the bottom, outboard edge of any existing improvement along property lines or roadway
fill. Once observed and approved, the bottom of the remedial grading excavations should
be lightly scarified, moisture conditioned (moisture added or dried back, as warranted) to
at least the soil’s optimum moisture content, and then be recompacted in accordance with
the recommendations in the “Fill Placement”section below. The use of vibratory
compaction equipment should not be considered for compaction, owing to the potential
for damage to neighboring improvements.
Earthwork Mitigation of Detrimentally Expansive Soils
As an alternative to using structural design for the mitigation of detrimentally expansive
soils, earthwork may be performed to remove any soils possessing an expansion index
(E.I.) greater than 20 and a plasticity index (P.I.) greater than 14, within the upper 7 feet of
pad grade, and replacing these soils with very low expansive (E.I. < 21) soil with a P.I. less
than 15. The lateral limits of the removal and replacement of detrimentally expansive soils
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should be at least 5 feet outside the perimeter footprint of the proposed residential
structure. This mitigation may reduce foundation requirements to possibly include
conventional foundations.
Alternating Slot Excavations
Remedial grading excavations extending below a 1½:1 (h:v) plane down from the bottom,
outboard edge of any existing improvements along property lines or the roadway fill should
be performed in alternating (A, B, and C) slots. Slot excavations should be a maximum of
6 feet in width. Multiple slots may be simultaneously excavated provided that open slots
are separated by at least 6 feet of engineered fill or undisturbed soils.
Perimeter Conditions
On a preliminary basis, any proposed settlement-sensitive improvements located within
approximately 17 to 20 feet from the property line on the east parcel, or within about
20 feet of the roadway fill, would likely require deepened foundations or additional
reinforcement by means of ground improvement or specific structural design, if remedial
grading in alternating slot or shored excavations is not performed. Otherwise, these
improvements may be subject to distress and a reduced serviceable lifespan. This would
require proper disclosure to all interested/affected parties should this condition exist at the
conclusion of grading.
Fill Placement
Following scarification of the bottom of the remedial grading excavation, the reused onsite
soils and import (if necessary) should be placed in ±6- to ±8-inch lifts, cleaned of
vegetation and debris, moisture conditioned (water added or dried back, as warranted) to
at least the soil’s optimum moisture content, and compacted to achieve a minimum relative
compaction of 90 percent of the laboratory standard (ASTM D 1557).
Overexcavation
Overexcavation should be performed minimally to 5-foot outside the building footprint or
a 1:1 (h:v) projection from the building to suitable bedrock, whichever is more.
Overexcavation should be completed to a depth of 2-foot below the lowest foundation
element. Since plans showing foundation layout and footing depths are currently
unavailable, the recommended overexcavation should be completed to at least 4 feet
below finish pad grade, on a preliminary basis. Overexcavated materials should be
replaced with engineered fill compacted to at least 90 percent of the laboratory standard
(ASTM D 1557). The bottom of the overexcavation should be sloped toward the parking
area or approved drainage facilities, scarified at least 6 to 8 inches, moisture-conditioned
as necessary to achieve the soil’s optimum moisture content, and then be recompacted
to at least 90 percent of the laboratory standard prior to fill placement. Overexcavation
should be completed across the entire building pad, as necessary, since building layouts
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are currently unknown. Overexcavations should be observed by the geotechnical
consultant prior to scarification. The maximum to minimum fill thickness across building
pads should not exceed a ratio of 3:1 (maximum:minimum).
Subdrains
Although generally not anticipated, local seepage along the contact between the fill lifts
may require subdrain systems, based on depth of fill, finish grade elevations, and potential
flowline outlet areas. Subdrains should consist of a 4-inch diameter perforated
Schedule 40 or SDR 35 drain pipe encased in 1 cubic foot of ¾-inch clean, crushed gravel,
and wrapped in filter fabric (Mirafi 140N or approved equivalent). Subdrains should outlet
into an approved drainage facility.
Earthwork Balance (Shrinkage/Bulking)
The volume change of excavated materials upon compaction as engineered fill is
anticipated to vary with material type and location. The overall earthwork shrinkage and
bulking may be approximated by using the following parameters:
Existing Artificial Fill .....................................0% to 10% shrinkage
Alluvium .............................................10% to 15% shrinkage
Santiago Formation ................................2% to 3% shrinkage or bulk
It should be noted that the above factors are estimates only, based on preliminary data.
Alluvium may achieve higher shrinkage if organics or clay content is higher than
anticipated. Final earthwork balance factors could vary. In this regard, it is recommended
that balance areas be reserved where grades could be adjusted up or down near the
completion of grading in order to accommodate any yardage imbalance for the project.
Subsidence in non-bedrock areas should be on the order of 0.1 feet.
Import Soils
If import fill is necessary, a sample of the soil import should be evaluated by this office prior
to importing, in order to assure compatibility with the onsite soils and the
recommendations presented in this report. If non-manufactured materials are used,
environmental documentation for the export site should be provided for GSI review. At
least three business days of lead time should be allowed by builders or contractors for
proposed import submittals. This lead time will allow for environmental document review,
particle size analysis, laboratory standard, expansion testing, and blended import/native
characteristics as deemed necessary. Import soils should be non-detrimentally expansive
(i.e., E.I. less than 21 and P.I. less than 15). The use of subdrains at the bottom of the fill
cap may be necessary, and may be subsequently recommended based on compatibility
with onsite soils.
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Slope Considerations and Slope Design
All slopes should be designed and constructed in accordance with the minimum
requirements of the City of Carlsbad, the 2013 CBC, and the recommendations in
Appendix G.
Temporary Slopes
Temporary slopes for excavations greater than 2 feet but less than 20 feet in overall height
should conform to CAL-OSHA and/or OSHA requirements for Type “B” soils, unless water
or seepage is present, or other adverse conditions are exposed, in which case Type “C”
soils would govern. Construction materials, soil stockpiles, and heavy equipment should
not be stored and/or operated within ‘H’ of any temporary slope where ‘H’ equals the
height of the temporary slope. All temporary slopes should be observed by a licensed
engineering geologist and/or geotechnical engineer prior to worker entry into the
excavation. Based on the exposed field conditions, inclining temporary slopes to flatter
gradients or the use of shoring or alternating slot excavations may be necessary if adverse
conditions are observed. The need for shoring or alternating slot excavations would be
best evaluated during the grading plan review stage and in the field during grading.
Excavation Observation and Monitoring (All Excavations)
When excavations are made adjacent to an existing improvement (i.e., utility, wall, road,
building, etc.) there is a risk of some damage even if a well designed system of excavation
is planned and executed. We recommend, therefore, that a systematic program of
observations be made before, during, and after construction to determine the effects (if
any) of construction on existing improvements.
We believe that this is necessary for two reasons: First, if excessive movements (i.e., more
than ½ inch) are detected early enough, remedial measures can be taken which could
possibly prevent serious damage to existing improvements. Second, the responsibility for
damage to the existing improvement can be determined more equitably if the cause and
extent of the damage can be determined more precisely.
Monitoring should include the measurement of any horizontal and vertical movements of
the existing structures/improvements. Locations and type of the monitoring devices should
be selected prior to the start of construction. The program of monitoring should be agreed
upon between the project team, the site surveyor and the Geotechnical
Engineer-of-Record, prior to excavation.
Reference points on existing walls, buildings, and other settlement-sensitive improvements.
These points should be placed as low as possible on the wall and building adjacent to the
excavation. Exact locations may be dictated by critical points, such as bearing walls or
columns for buildings; and surface points on roadways or curbs near the top of the
excavation.
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For a survey monitoring system, an accuracy of a least 0.01 foot should be required.
Reference points should be installed and read initially prior to excavation. The readings
should continue until all construction below ground has been completed and the
permanent backfill has been brought to final grade.
The frequency of readings will depend upon the results of previous readings and the rate
of construction. Weekly readings could be assumed throughout the duration of
construction with daily readings during rapid excavation near the bottom of the excavation.
The reading should be plotted by the Surveyor and then reviewed by the Geotechnical
Engineer. In addition to the monitoring system, it would be prudent for the Geotechnical
Engineer and the Contractor to make a complete inspection of the existing structures both
before and after construction. The inspection should be directed toward detecting any
signs of damage, particularly those caused by settlement. Notes should be made and
pictures should be taken where necessary.
Observation
It is recommended that all excavations be observed by the Geologist and/or Geotechnical
Engineer. Any fill which is placed should be approved, tested, and verified if used for
engineered purposes. Should the observation reveal any unforseen hazard, the Geologist
or Geotechnical Engineer will recommend treatment. Please inform GSI at least 24 hours
prior to any required site observation.
PRELIMINARY FOUNDATION RECOMMENDATIONS - ALTERNATIVE A
General
The preliminary foundation design and construction recommendations, presented herein,
are based on the geotechnical data obtained during our recent field studies, laboratory
testing of the onsite earth materials, and engineering evaluations performed in conjunction
with this investigation. The following preliminary foundation design and construction
recommendations are presented as minimum criteria from a geotechnical engineering
viewpoint.
This section presents minimum design criteria for the design of foundations, concrete
slab-on-grade floors, and other elements possibly applicable to the project. These criteria
should not be considered as substitutes for actual designs by the structural engineer.
Recommendations by the project's design-structural engineer or architect, which may
exceed the geotechnical consultant’s recommendations, should take precedence over the
following minimum requirements. The foundation systems recommended herein may be
used to support the proposed residential structure provided they are entirely founded in
engineered fill tested and approved by GSI that overlies dense formational earth materials.
Foundation and slab-on-grade floor systems constructed within the influence of
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detrimentally expansive soils (E.I. > 20 and P.I. > 14 [such as exists at the site]) should
be designed in accordance with Section 1808.6.2 of the 2013 CBC.
In the event that the information concerning the proposed development plan is not correct,
or any changes in the design, location or loading conditions of the proposed structure are
made, the conclusions and recommendations contained in this report shall not be
considered valid unless the changes are reviewed and conclusions of this report are
modified or approved in writing by this office. Upon request, GSI could provide additional
input/consultation regarding soil parameters, as they relate to foundation design
Based on the onsite soil conditions, anticipated loading conditions, and use (i.e.,
improvements), we have considered conventional shallow spread footings, a
post-tensioned slab, and a mat-type foundation to be appropriate foundation designs from
a geotechnical perspective, provided unsuitable soils are removed and recompacted, as
indicated herein.
General Foundation Design
1.The foundation systems should be designed and constructed in accordance with
guidelines presented in the 2013 CBC.
2.An allowable bearing value of 2,000 psf may be used for the design of continuous
spread footings that maintain a minimum width of 12 inches and a minimum depth
of 12 inches below the lowest adjacent grade or isolated spread footings having a
minimum dimension of 24 inches and a minimum embedment of 24 inches below
the lowest adjacent grade. Footings should be entirely founded into properly
engineered fill overlying dense formational materials. This value may be increased
by 20 percent for each additional 12 inches in footing embedment to a maximum
value of 2,500 psf. These values may also be increased by one-third when
considering short duration seismic or wind loads. Foundation embedment excludes
any landscaped zones, concrete slabs-on-grade, and/or slab underlayment.
Allowable bearing values for post-tensioned slab and mat foundations are provided
in their respective sections.
3.The passive earth pressure may be computed as an equivalent fluid having a
density of 200 pcf, with a maximum earth pressure of 2,000 psf for footings founded
into properly engineered fill. Lateral passive pressures for shallow foundations
within 2013 CBC setback zones or within the influence of retaining walls should be
reduced following a review by the geotechnical engineer unless proper setbacks
can be established.
4.For lateral sliding resistance, a 0.35 coefficient of friction may be utilized for a
concrete to soil contact when multiplied by the dead load.
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5.When combining passive pressure and frictional resistance, the passive pressure
component should be reduced by one-third.
6.All footing setbacks from slopes should comply with Figure 1808.7.1 of the
2013 CBC. GSI recommends a minimum horizontal setback distance of 7 feet as
measured from the bottom (i.e., bearing elevation), outboard edge of the footing to
any slope face.
7.Footings for structures adjacent to retaining walls should be deepened so as to
extend below a 1:1 projection from the heel of the wall should this condition occur.
Alternatively, walls may be designed to accommodate structural loads from
buildings or appurtenances as described in the “Retaining Wall” section of this
report.
8.All interior and exterior column footings should be tied to the perimeter wall footings
in at least two directions. The base of the reinforced grade beam should be at the
same elevation as the adjoining footings.
Preliminary Foundation and Fill Settlements - Alternative A
In addition to designing foundations for the corrosive and expansive soil conditions
described herein, the estimated vertical settlement and angular distortion values that an
individual structure (including walls, footings, and/or other settlement-sensitive
improvements, etc.), could be subjected to should be evaluated by a structural engineer.
The levels of angular distortion were evaluated on a 40-foot length assumed as the
minimum dimension of building spans; if, from a structural standpoint, a decreased or
increased length over which the differential settlement is assumed to occur is justified, this
change should be incorporated into the design. Typical differential foundation settlement
generally occurs between the lightest and heaviest foundation elements. Provided that the
Alternative “A” earthwork recommendations are implemented, differential settlement of up
to approximately 1 inch over 40 feet horizontally (i.e., angular distortion approximately
1/480), may be assumed. Differential vertical settlements of 1 inch in 30 feet (about 1/350)
should be applied between the heaviest and lightest foundation elements (i.e., between
heaviest columns or wall footings). These localized static settlements are anticipated to
be mostly complete at the conclusion of construction.
Any post-construction settlement of the fill should be mitigated by proper foundation
design, provided the design parameters, provided in this report, are properly utilized in
final design of foundation system(s). In addition to the above, the structural engineer
should also consider estimated settlements due to short duration seismic loading and
applicable load combinations, as required by the City and/or the 2013 CBC (CBSC, 2013).
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Preliminary Conventional Foundation and Slab-On-Grade Construction
Recommendations - Non Detrimentally Expansive Soils
The following recommendations are for conventional foundations and slab-on-grade floor
systems underlain by at least 7 feet of non-detrimentally expansive engineered fill (i.e., E.I.
< 21 and P.I. < 15) overlying dense, unweathered Santiago Formation. This would likely
require selective grading and/or import to accomplish. The structural engineer’s
recommendations may be more onerous, based on actual floor loads.
1.Exterior and interior footings should be founded into approved engineered fill at a
minimum depth of 12, 18, or 24 inches below the lowest adjacent grade for a one-,
two-, or three-story floor loads, respectively. For one-, two-, and three-story floor
loads, footing widths should be at least 12, 15, and 18 inches, respectively.
Isolated, exterior column and panel pads, or wall footings, should be at least
24 inches square, and founded at a minimum depth of 24 inches into approved
engineered fill. All footings should be minimally reinforced with four No. 4
reinforcing bars, two placed near the top and two placed near the bottom of the
footing. Depth of embedment does not include the slab or underlayment thickness,
and is measured from the lowest adjacent grade.
2.All interior and exterior column footings, and perimeter wall footings, should be tied
together via grade beams in at least one direction, for very low expansive soils, or
two directions otherwise. The grade beams should be at least 12 inches square in
cross section, and should be provided with a minimum of one No.4 reinforcing bar
near the top, and one No.4 reinforcing bar near the bottom of the grade beam. The
base of the reinforced grade beams should be at the same elevation as the
adjoining footings. A stepped grade beam, constructed per the structural
engineer’s specifications, may be necessary where the base of footings occur at
different elevations.
3.A grade beam, reinforced as previously recommended and at least 12 inches
square, should be provided across large (garage) entrances. The base of the
reinforced grade beam should be at the same elevation as the adjoining footings.
A stepped grade beam, constructed per the structural engineer’s specifications,
may be necessary where the base of footings occur at different elevations.
4.A minimum concrete slab-on-grade floor thickness of 4.5 inches is recommended.
A maximum water to cement ratio of 0.5 is recommended for foundations and
slab-on-grade floors.
5.Concrete slabs should be reinforced with a minimum of No. 3 reinforcement bars
placed at 18 inches on center, in two horizontally perpendicular directions (i.e., long
axis and short axis).
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6.The actual thickness and steel reinforcement for concrete slab-on-grade floors
should be determined by the project structural engineer, based on the anticipated
loading conditions and building use. However, the slab thickness and steel
reinforcement, recommended above, are considered minimum guidelines.
7.All slab reinforcement should be supported to ensure proper mid-slab height
positioning during placement of the concrete. "Hooking" of reinforcement is not an
acceptable method of positioning.
8.Slab subgrade pre-soaking is not required for non-detrimentally expansive soil
conditions. However, the Client should consider pre-wetting the slab subgrade
materials to at least the soil’s optimum moisture content to a minimum depth of
12 inches, within 72 hours of the placement of the underlayment sand and vapor
retarder.
9.Soils generated from footing excavations to be used onsite should be compacted
to a minimum relative compaction of 90 percent of the laboratory standard
(ASTM D 1557), whether the soils are to be placed inside the foundation perimeter
or in the yard/right-of-way areas. This material must not alter positive drainage
patterns that direct drainage away from the structural areas and toward traffic areas
or approved drainage facilities.
Post-Tensioned Slab Foundation Systems
Post-tensioned slab foundations may be used to mitigate the damaging shrink/swell effects
of expansive soils that exist onsite. The post-tensioned slab foundation designer may elect
to exceed the minimal recommendations, provided herein, to increase slab stiffness
performance. Post-tension (PT) design may be either ribbed or mat-type. The latter is also
referred to as uniform thickness foundation (UTF). The use of a UTF is an alternative to the
traditional ribbed-type. The UTF offers a reduction in grade beams. That is to say a UTE
typically uses a single perimeter grade beam and possible “shovel” footings, but has a
thicker slab than the ribbed-type.
The information and recommendations presented in this section are not meant to
supercede design by a registered structural engineer or civil engineer qualified to perform
post-tensioned slab foundation design. Post-tensioned foundations should be designed
using sound engineering practice and be in accordance with local and
2013 CBC requirements. Upon request, GSI can provide additional data/consultation
regarding soil parameters as related to post-tensioned foundation design. For the purpose
of this study, GSI is providing recommended post-tensioned slab foundation design criteria
for low, medium and highly expansive soil conditions (E.I. = 21 to 130).
From a soil expansion/shrinkage standpoint, a common contributing factor to distress of
structures using post-tensioned slabs is a "dishing" or "arching" of the slabs. This is caused
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by the fluctuation of moisture content in the soils below the perimeter of the slab primarily
due to onsite and offsite irrigation practices, climatic and seasonal changes, and the
presence of expansive soils. When the soil environment surrounding the exterior of the
slab has a higher moisture content than the area beneath the slab, moisture tends to
migrate inward, underneath the slab edges to a distance beyond the slab edges referred
to as the moisture variation distance. When this migration of water occurs, the volume of
the soils beneath the slab edges expands and causes the slab edges to lift in response.
This is referred to as an edge-lift condition. Conversely, when the outside soil environment
is drier, the moisture transmission regime is reversed and the soils underneath the slab
edges lose their moisture and shrink. This process leads to dropping of the slab at the
edges, which leads to what is commonly referred to as the center lift condition. A
well-designed, post-tensioned slab having sufficient stiffness and rigidity provides a
resistance to excessive bending that results from non-uniform swelling and shrinking slab
subgrade soils, particularly within the moisture variation distance, near the slab edges.
Other mitigation techniques typically used in conjunction with post-tensioned slabs consist
of a combination of specific soil pre-saturation and the construction of a perimeter "cut-off"
wall grade beam. Soil pre-saturation consists of moisture conditioning the slab subgrade
soils prior to the post-tension slab construction. This effectively reduces soil moisture
migration from the area located outside the building toward the soils underlying the
post-tension slab. Perimeter cut-off walls are thickened edges of the concrete slab that
impedes both outward and inward soil moisture migration.
Slab Subgrade Pre-Soaking
Pre-moistening of the slab subgrade soil is recommended for detrimentally expansive soil
conditions. The moisture content of the subgrade soils should be equal to or greater than
optimum moisture to a depth equivalent to the perimeter grade beam or cut-off wall depth
in the slab areas (typically 12, 18 and 24 inches) for low, medium and high expansive soil
conditions.
Pre-moistening and/or pre-soaking should be evaluated by the soils engineer 72 hours
prior to vapor retarder placement. In summary:
EXPANSION
POTENTIAL PAD SOIL MOISTURE CONSTRUCTION
METHOD
SOIL MOISTURE
RETENTION
Low
(21-50)
Upper 12 inches of pad soil
moisture 2 percent over
optimum (or 1.2 times)
Wetting and/or
reprocessing
Periodically wet or cover
with plastic after trenching.
Evaluation 72 hours prior to
placement of concrete.
Medium
(E.I. = 51-90)
Upper 18 inches of pad soil
moisture 2 percent over
optimum (or 1.2 times)
Berm and flood or wetting
and reprocessing
Periodically wet or cover
with plastic after trenching.
Evaluation 72 hours prior to
placement of concrete.
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EXPANSION
POTENTIAL PAD SOIL MOISTURE CONSTRUCTION
METHOD
SOIL MOISTURE
RETENTION
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High
(E.I. = 91-130)
Upper 24 inches of pad soil
moisture 3 percent over
optimum (or 1.3 times)
Berm and flood or wetting
and reprocessing
Periodically wet or cover
with plastic after trenching.
Evaluation 72 hours prior to
placement of concrete.
Perimeter Cut-Off Walls
Perimeter cut-off walls should be at least 12, 18 or 24 inches deep for low, medium or
highly expansive soil conditions, respectively. The cut-off walls may be integrated into the
slab design or independent of the slab. The cut-off walls should be a minimum of 6 inches
thick (wide). The bottom of the perimeter cut-off wall should be designed to resist tension,
using cable or reinforcement per the structural engineer.
Post-Tensioned Foundation Design
The following recommendations for design of post-tensioned slabs have been prepared
in general compliance with the requirements of the recent Post Tensioning Institute’s
(PTI’s) publication titled “Design of Post-Tensioned Slabs on Ground, Third Edition”
(PTI, 2004), together with it’s subsequent addendums (PTI, 2008).
Soil Support Parameters
The recommendations for soil support parameters have been provided based on the
typical soil index properties for soils that are medium to high in expansion potential. The
soil index properties are typically the upper bound values based on our experience and
practice in the southern California area. Additional testing is recommended either during
or following grading, and prior to foundation construction to further evaluate the soil
conditions within the upper 7 to 15 feet of pad grade. The following table presents
suggested minimum coefficients to be used in the Post-Tensioning Institute design
method.
Thornthwaite Moisture Index -20 inches/year
Correction Factor for Irrigation 20 inches/year
Depth to Constant Soil Suction 7 feet or overexcavation
depth to bedrock
Constant soil Suction (pf)3.6
Moisture Velocity 0.7 inches/month
Effective Plasticity Index (P.I.)*25-35
* - The effective plasticity index should be evaluated for the upper 7 to
15 feet of foundation soils either during or following grading.
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Based on the above, the recommended soil support parameters are tabulated below:
DESIGN PARAMETERS LOW EXPANSION
(E.I. = 21-50)
MEDIUM EXPANSION
(E.I. = 51-90)
HIGH EXPANSION
(E.I. = 91-130)
me center lift 9.0 feet 8.7 feet 8.5 feet
me edge lift 5.2 feet 4.5 feet 4.0 feet
my center lift 0.4 inches 0.5 inches 0.66 inches
my edge lift 0.7 inch 1.3 inch 1.7 inches
Bearing Value 1,000 psf 1,000 psf 1,000 psf(1)
Lateral Pressure 250 psf 175 psf 150 psf
Subgrade Modulus (k)100 pci/inch 85 pci/inch 70 pci/inch
Minimum Perimeter
Footing Embedment (2)12 inches 18 inches 24 inches
Internal bearing values within the perimeter of the post-tension slab may be increased to 1,500 psf for a minimum(1)
embedment of 12 inches, then by 20 percent for each additional foot of embedment to a maximum of 2,500 psf.
As measured below the lowest adjacent compacted subgrade surface without landscape layer or sand(2)
underlayment.
Note: The use of open bottomed raised planters adjacent to foundations will require more onerous design parameters.
Preliminary Foundation Design and Construction Recommendations for Mat-Type
Foundations - Alternative A
Mat-type foundations and slabs may be utilized to mitigate the effects of expansive soils.
For mat foundations founded at least 18 inches in properly compacted engineered fill, a
maximum allowable bearing capacity of 2,500 psf is recommended. This value may be
increased by one-third for short-term loads including wind or seismic. Reinforcement
should be designed in accordance with local codes and structural considerations.
Mat-type foundations or slabs may be uniform thickness or incorporate edge footings for
moisture cut-off barriers as recommended herein. Edge footings should be at least
12 inches wide and extend 18 inches below the lowest adjacent grade. The bottom of the
edge footing should be designed to resist tension, using reinforcement per the structural
engineer. The need and arrangement of interior grade beams (stiffening beams) will be
in accordance with the structural consultant’s recommendations. Uniform thickness mat
foundations/slabs should extend at least 18 inches below the lowest adjacent grade.
Reinforcement bar sizing and spacing for mat foundations should be provided by the
structural engineer. The parameters herein should be modified to mitigate the effects of
the differential settlements reported earlier in this report.
Mat Foundation Design
The design of mat foundations should incorporate the vertical modulus of subgrade
reaction. This value is a unit value for a 1-foot square footing and should be reduced in
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accordance with the following equation when used with the design of larger foundations.
This is assumes that the bearing soils will consist of engineered fills with an average
relative compaction of 90 percent of the laboratory (ASTM D 1557), overlying dense
formational earth materials.
S where: K = unit subgrade modulus
R K = reduced subgrade modulus
B = foundation width (in feet)
SThe modulus of subgrade reaction (K ) and effective plasticity index (PI) to be used in mat
foundation design for various expansive soil conditions are presented in the following
table. The effective plasticity index for the upper 7 to 15 feet of the foundation soils should
be evaluated during or following grading. Lateral pressures for mat foundation design
should conform to those previously provided in the “Post-Tensioned Slab Foundation
Systems” section of this report.
LOW EXPANSION
(E.I. = 0-50)
MEDIUM EXPANSION
(E.I. = 51-90)
HIGH EXPANSION
(E.I. = 91-130)
SS SK =100 pci/inch, P.I. <15 K =85 pci/inch, P.I. = 25 K =70 pci/inch, P.I. = 35
Slab Subgrade Moisture Content
Pre-moistening/per-soaking of the slab subgrade soil is recommended owing to expansive
soil conditions at the site. The moisture content of the subgrade soils should be equal to
or greater than optimum moisture to a depth equivalent to the perimeter grade beam or
cut-off wall depth in the slab areas (typically 12, 18 and 24 inches for low, medium and
highly expansive soil conditions, respectively). Pre-moistening and/or pre-soaking should
be evaluated by the soils engineer 72 hours prior to vapor retarder placement.
DRILLED PIER AND GRADE BEAM
FOUNDATION RECOMMENDATIONS (ALTERNATIVE B)
Alternative B is primarily for the east parcel. The proposed residential structure, underlain
by left in-place undocumented fill, roadway fill, alluvium, and weathered Santiago
Formation may be supported by drilled, cast-in-place, concrete piers with structural
concrete floors. All drilled piers should extend a minimum of 5 feet into competent
formational materials, or a minimum tip elevation of 70 feet, on a preliminary basis. Actual
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pier embedment should be finalized by the project’s structural engineer. The structural
strength of the piers should be checked by the structural engineer or civil engineer
specializing in structural analysis. Pier holes should be drilled straight and plumb.
Locations (both plan and elevation) and plumbness should be the contractors
responsibility.
The grade beam should be at a minimum of 24 inches by 24 inches in cross section and
supported by drilled piers 24 inches in diameter which are placed at a minimum spacing
of 8 to 10 feet on center and supporting all structural columns. The design of the grade
beam and caissons should be in accordance with the recommendations of the project
structural engineer, and utilize the following geotechnical parameters:
Passive Resistance
Passive earth pressure of 400 lbs/ft per foot of pier depth, to a maximum value of 4,000 psf2
may be used to determine pier depth and spacing, provided that they meet or exceed the
minimum requirements stated above.
Point of Fixity
The point of fixity should be located at approximately 1 pier diameter below the top of the
unweathered Santiago Formation, or approximately 16 to 19 feet below the existing grade,
on the east parcel.
Allowable Axial Capacity
A shaft capacity of 400 psf should be applied over the surface area of the drilled pier
located in the unweathered Santiago Formation only. The tip bearing capacity should be
limited to 4,000 psf.
Caisson Construction
1.The excavation and installation of the drilled piers should be observed and
documented by the project geotechnical engineer to verify the recommended
embedment depth.
2.The drilled holes should be cased, specifically below the water table to prevent
caving. The bottom of the casing should be at least 4 feet below the top of the
concrete as the concrete is poured and the casing is withdrawn. Dewatering may
be required for concrete placement. This should be considered during project
planning. The bottom of the drilled pier should be cleared of any loose or soft soils
before concrete placement.
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3.The exact depths of the piers should be determined during the final precise grading
plan review.
4.Proper slump underwater type concrete with a maximum water to cement ratio of
0.50 should be used, and should be delivered through a tremie pipe. We
recommend that concrete be placed through the tremie pipe immediately
subsequent to approved excavation and steel placement. Care should be taken to
prevent striking the walls of the excavations with the tremie pipe during concrete
placement.
5.Drilled pier steel reinforcement cages should have spacers to allow for a minimum
spacing of steel from the side of the pier excavation. The need for corrosion
protected reinforcing steel in drilled pier construction should be evaluated by the
structural consultant.
6.During pier placement, concrete should not be allowed to free fall more than 5 feet.
7.Concrete used in the foundation should be tested by a qualified materials testing
consultant for strength and mix design.
Drilled Pier and Grade Beam Foundation Settlement
Drilled pier and grade beam foundations should be designed to accommodate a
differential settlement of ½ inch over a 40-foot horizontal span.
Corrosion and Concrete Mix
Upon completion of grading, laboratory testing should be performed of site materials for
corrosion to concrete and corrosion to steel. Additional comments may be obtained from
a qualified corrosion engineer at that time.
SOIL MOISTURE TRANSMISSION CONSIDERATIONS (BOTH ALTERNATIVES)
GSI has evaluated the potential for vapor or water transmission through concrete floor
slabs, in light of typical floor coverings and improvements. Please note that slab moisture
emission rates range from about 2 to 27 lbs/24 hours/1,000 square feet from a typical slab
(Kanare, 2005), while floor covering manufacturers generally recommend about
3 lbs/24 hours as an upper limit. The recommendations in this section are not intended
to preclude the transmission of water or vapor through the foundation or slabs.
Foundation systems and slabs shall not allow water or water vapor to enter into the
structure so as to cause damage to another building component or to limit the installation
of the type of flooring materials typically used for the particular application (State of
California, 2016). These recommendations may be exceeded or supplemented by a water
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“proofing” specialist, project architect, or structural consultant. Thus, the client will need
to evaluate the following in light of a cost vs. benefit analysis (owner expectations and
repairs/replacement), along with disclosure to all interested/affected parties. It should also
be noted that vapor transmission will occur in new slab-on-grade floors as a result of
chemical reactions taking place within the curing concrete. Vapor transmission through
concrete floor slabs as a result of concrete curing has the potential to adversely affect
sensitive floor coverings depending on the thickness of the concrete floor slab and the
duration of time between the placement of concrete, and the floor covering. It is possible
that a slab moisture sealant may be needed prior to the placement of sensitive floor
coverings if a thick slab-on-grade floor is used and the time frame between concrete and
floor covering placement is relatively short.
Considering the known soil conditions in the region, the anticipated typical water vapor
transmission rates, floor coverings, and improvements (to be chosen by the Client and/or
project architect) that can tolerate vapor transmission rates without significant distress, the
following alternatives are provided:
•Concrete slabs, including the garage slab, should be thickened.
•Concrete slab underlayment should consist of a 15-mil vapor retarder, or equivalent,
with all laps sealed per the 2013 CBC and the manufacturer’s recommendation.
The vapor retarder should comply with the ASTM E 1745 - Class A criteria (Stego
Wrap or approved equivalent), and be installed in accordance with ACI 302.1R-04
and ASTM E 1643.
•The 15-mil vapor retarder (ASTM E 1745 - Class A) shall be installed per the
recommendations of the manufacturer, including all penetrations (i.e., pipe, ducting,
rebar, etc.).
•Concrete slabs, including the garage slab, should be underlain by 2 inches of clean,
washed sand (SE > 30) above a 15-mil vapor retarder (ASTM E-1745 - Class A, per
Engineering Bulletin 119 [Kanare, 2005]) installed per the recommendations of the
manufacturer, including all penetrations (i.e., pipe, ducting, rebar, etc.). The
manufacturer shall provide instructions for lap sealing, including minimum width of
lap, method of sealing, and either supply or specify suitable products for lap sealing
(ASTM E 1745), and per code.
ACI 302.1R-04 (2004) states “If a cushion or sand layer is desired between the
vapor retarder and the slab, care must be taken to protect the sand layer from
taking on additional water from a source such as rain, curing, cutting, or cleaning.
Wet cushion or sand layer has been directly linked in the past to significant
lengthening of time required for a slab to reach an acceptable level of dryness for
floor covering applications.” Therefore, additional observation and/or testing will be
necessary for the cushion or sand layer for moisture content, and relatively uniform
thicknesses, prior to the placement of concrete.
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•For very low expansive soil conditions (E.I. < 21 and P.I. < 15), the vapor retarder
should be underlain by 2 inches of sand (SE > 30) placed directly on the prepared,
moisture conditioned, subgrade and should be sealed to provide a continuous
retarder under the entire slab, as discussed above. The underlying sand layer may
be omitted provided testing indicates the SE of the slab subgrades soils is greater
than or equal to 30. If the slab subgrade exposes soils with an E.I. > 20 and P.I. >
14, the vapor retarder shall be underlain by a capillary break consisting of at least
4 inches of clean crushed gravel with a maximum dimension of ¾ inch (less than
5 percent passing the No. 200 sieve).
•The maximum water to cement ratio for concrete used in foundation and
slab-on-grade floor construction should not exceed 0.50. Additional concrete mix
design recommendations should be provided by the structural consultant and/or
waterproofing specialist. Concrete finishing and workablity should be addressed
by the structural consultant and a waterproofing specialist.
•Where slab water/cement ratios are as indicated herein, and/or admixtures used,
the structural consultant should also make changes to the concrete in the grade
beams and footings in kind, so that the concrete used in the foundation and slabs
are designed and/or treated for more uniform moisture protection.
•The homeowner should be specifically advised which areas are suitable for tile
flooring, vinyl flooring, or other types of water/vapor-sensitive flooring and which
areas are not suitable for these types of flooring applications. In all planned floor
areas, flooring shall be installed per the manufactures recommendations.
•Additional recommendations regarding water or vapor transmission should be
provided by the architect/structural engineer/slab or foundation designer and
should be consistent with the specified floor coverings indicated by the architect.
Regardless of the mitigation, some limited moisture/moisture vapor transmission through
the slab cannot be entirely precluded and should be anticipated. Construction crews may
require special training for installation of certain product(s), as well as concrete finishing
techniques. The use of specialized product(s) should be approved by the slab designer
and water-proofing consultant. A technical representative of the flooring contractor should
review the slab and moisture retarder plans and provide comment prior to the construction
of the foundation or improvement. The vapor retarder contractor should have
representatives onsite during the initial installation.
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WALL DESIGN PARAMETERS
General
The following recommendations for the design and construction of conventional masonry
retaining walls have been provided should they be included into the proposed
development plan. Recommendations for specialty walls (i.e., crib, earthstone, geogrid,
etc.) can be provided upon request, and would be based on site-specific conditions.
Conventional Retaining Walls
The design parameters, provided below, assume that either very low expansive soils
(typically Class 2 permeable filter material or Class 3 aggregate base) or native onsite
materials with an E.I. up to 20 and a P.I. less than 15 are used to backfill any retaining wall
(this latter case would require significant compliance testing). The type of backfill (i.e.,
select or native), should be specified by the wall designer, and clearly shown on the plans.
Any building walls, below grade (i.e., basement walls), should be water-proofed.
Waterproofing should also be provided for site retaining walls in order to reduce the
potential for efflorescence staining.
Preliminary Retaining Wall Foundation Design
Preliminary foundation design for retaining walls should incorporate the following
recommendations:
Minimum Footing Embedment - 24 inches below the lowest adjacent grade
(excluding landscape layer, 6 inches).
Minimum Footing Width - 24 inches
Allowable Bearing Pressure - An allowable bearing pressure of 2,500 pcf may be
used in the preliminary design of retaining wall foundations provided that the footing
maintains a minimum width of 24 inches and extends at least 24 inches into
approved engineered fill overlying dense unweathered formational deposits. This
pressure may be increased by one-third for short-term wind and/or seismic loads.
Passive Earth Pressure - A passive earth pressure of 200 pcf with a maximum
earth pressure of 2,000 psf may be used in the preliminary design of retaining wall
foundations.
Lateral Sliding Resistance - A 0.35 coefficient of friction may be utilized for a
concrete to soil contact when multiplied by the dead load. When combining
passive pressure and frictional resistance, the passive pressure component should
be reduced by one-third.
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Soil Density - Soil densities ranging between 110 pcf and 120 pcf may be used in
the design of retaining wall foundations. This assumes an average engineered fill
compaction of at least 90 percent of the laboratory standard.
Any retaining walls near the perimeter of the site will likely need to be supported by drilled
pier and grade beam foundations systems for adequate vertical and lateral bearing
support. All retaining wall footing setbacks from any slopes should comply with
Figure 1808.7.1 of the 2013 CBC. GSI recommends a minimum horizontal setback
distance of 7 feet as measured from the bottom, outboard edge of the footing to any slope
face.
Restrained Walls
Any retaining walls that will be restrained prior to placing and compacting backfill material
or that have re-entrant or male corners, should be designed for an at-rest equivalent fluid
pressure (EFP) of 55 pcf and 65 pcf for select and very low expansive native backfill,
respectively. The design should include any applicable surcharge loading. For areas of
male or re-entrant corners, the restrained wall design should extend a minimum distance
of twice the height of the wall (2H) laterally from the corner.
Cantilevered Walls
The recommendations, presented below, are for cantilevered retaining walls up to 10 feet
high. Design parameters for walls less than 3 feet in height may be superceded by
San Diego regional standard design. Active earth pressure may be used for retaining wall
design, provided the top of the wall is not restrained from minor deflections. An equivalent
fluid pressure approach may be used to compute the horizontal pressure against the wall.
Appropriate fluid unit weights are given below for specific slope gradients of the retained
material. These do not include other superimposed loading conditions due to traffic,
structures, seismic events or adverse geologic conditions. When wall configurations are
finalized, the appropriate loading conditions for superimposed loads can be provided upon
request.
For preliminary planning purposes, the structural consultant should incorporate the
surcharge of traffic on the back of retaining walls where vehicular traffic will occur within
a horizontal distance equal to “H” from the back of any retaining wall (where “H” equals
the height of the retaining wall). The traffic surcharge may be taken as 100 psf/ft in the
upper 5 feet of backfill for light truck and car traffic. This does not include the surcharge
of parked vehicles which should be evaluated at a higher surcharge to account for the
effects of seismic loading.
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SURFACE SLOPE OF
RETAINED MATERIAL
(HORIZONTAL:VERTICAL)
EQUIVALENT
FLUID WEIGHT P.C.F.
(SELECT BACKFILL)(2)
EQUIVALENT
FLUID WEIGHT P.C.F.
(NATIVE BACKFILL)(3)
Level(1)
2 to 1
38
55
45
60
Level backfill behind a retaining wall is defined as compacted earth materials, properly drained, without(1)
a slope for a distance of 2H behind the wall, where H is the height of the wall.
SE > 30, P.I. < 15, E.I. < 21, and < 10% passing No. 200 sieve.(2)
E.I. = 0 to 20, SE > 25, P.I. < 15, and < 15% passing No. 200 sieve.(3)
Seismic Surcharge
For engineered retaining walls where the height of retained earth is 6 feet or greater, or
incorporated into a building, and/or could pose ingress or egress constraints to the
residential structure, GSI recommends that such walls be evaluated for a seismic
surcharge (in general accordance with 2013 CBC requirements). The site walls in this
category should maintain an overturning Factor-of-Safety (FOS) of approximately 1.25
when the seismic surcharge (increment), is applied. This seismic surcharge pressure
(seismic increment) may be taken as 15H where "H" is the height of the retained backfill,
measured from the top of the footing at its heel. The resultant force should be applied at
a distance 0.6 H up from the bottom of the footing. For restrained walls, the seismic
surcharge should be applied as a uniform surcharge load from the bottom of the footing
(excluding shear keys) to the top of the backfill at the heel of the wall footing. For
cantilevered walls, the pressure should be an inverted triangular distribution using 15H.
The bearing pressure obtained during the seismic evaluation may exceed the static value
by one-third, considering the transient nature of this surcharge. Please note this is for local
wall stability only.
The 15H is derived from a Mononobe-Okabe solution for both restrained cantilever walls.
This accounts for the increased lateral pressure due to shakedown or movement of the
sand fill soil in the zone of influence from the wall or roughly a 45/ - N/2 plane away from
the back of the wall. The 15H seismic surcharge is derived from the formula:
hhtP = d C a C (H
hWhere:P =Seismic increment
ha =Probabilistic horizontal site acceleration with a percentage of
“g”
t(=total unit weight (115 to 125 pcf for site soils @ 90% relative
compaction).
H=Height of the wall from the bottom of the footing or point of pile
fixity.
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Retaining Wall Backfill and Drainage
Positive drainage must be provided behind all retaining walls in the form of gravel wrapped
in geofabric and outlets. A backdrain system is considered necessary for retaining walls
that are 2 feet or greater in height. Details 1, 2, and 3, present the backdrainage options
discussed below. Backdrains should consist of a 4-inch diameter perforated PVC or ABS
pipe encased in either Class 2 permeable filter material or ¾-inch to 1½-inch gravel
wrapped in approved filter fabric (Mirafi 140 or equivalent). The backdrain should flow via
gravity (minimum 1 percent fall) toward an approved drainage facility selected by a civil
engineer. For select backfill, the filter material should extend a minimum of 1 horizontal
foot behind the base of the walls and upward at least 1 foot. For native backfill that has up
to E.I. = 20, continuous Class 2 permeable drain materials should be used behind the wall.
This material should be continuous (i.e., full height) behind the wall, and it should be
constructed in accordance with the enclosed Detail 1 (Typical Retaining Wall Backfill and
Drainage Detail). For limited access and confined areas, (panel) drainage behind the wall
may be constructed in accordance with Detail 2 (Retaining Wall Backfill and Subdrain
Detail Geotextile Drain). Materials with an expansion index (E.I.) potential of greater than
20 should not be used as backfill for retaining walls. For more onerous expansive
situations, backfill and drainage behind the retaining wall should conform with Detail 3
(Retaining Wall And Subdrain Detail Clean Sand Backfill). Retaining wall backfill should
be moisture conditioned to 1.1 to 1.2 times the soil’s optimum moisture content, placed
in relatively thin lifts, and compacted to at least 90 percent of the laboratory standard
(ASTM D 1557).
Outlets should consist of a 4-inch diameter solid PVC or ABS pipe spaced no greater than
±100 feet apart, with a minimum of two outlets, one on each end. The use of weep holes,
only, in walls higher than 2 feet, is not recommended. The surface of the backfill should
be sealed by pavement or the top 18 inches compacted with native soil (E.I. # 50). Proper
surface drainage should also be provided. For additional mitigation, consideration should
be given to applying a water-proof membrane to the back of all retaining structures. The
use of a waterstop should be considered for all concrete and masonry joints.
Wall/Retaining Wall Footing Transitions
Site walls are anticipated to be founded on footings designed in accordance with the
recommendations in this report. Should wall footings transition from cut to fill, the civil
designer may specify either:
a)A minimum of a 2-foot overexcavation and recompaction of cut materials for a
distance of 2H, from the point of transition.
b)Increase of the amount of reinforcing steel and wall detailing (i.e., expansion joints
or crack control joints) such that a angular distortion of 1/360 for a distance of 2H
on either side of the transition may be accommodated. Expansion joints should be
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placed no greater than 20 feet on-center, in accordance with the structural
engineer’s/wall designer’s recommendations, regardless of whether or not transition
conditions exist. Expansion joints should be sealed with a flexible, non-shrink grout.
c) Embed the footings entirely into native formational material (i.e., deepened
footings).
If transitions from cut to fill transect the wall footing alignment at an angle of less than
45 degrees (plan view), then the designer should follow recommendation "a" (above) and
until such transition is between 45 and 90 degrees to the wall alignment.
TEMPORARY SHORING DESIGN AND CONSTRUCTION
Shoring of Excavations
GSI is providing the following recommendations should temporary shoring be necessary
in order to temporarily retain existing offsite improvements that are to remain in serviceable
during the recommended remedial grading excavations (Alternative “A”). GSI anticipates
that a system of cast-in-place soldier beams and wood lagging, would be necessary to
retain excavation walls if the temporary slopes, recommended herein, would extend into
offsite property or would pass below a 1½:1 projection down from the bottom outboard
edge of any offsite improvement that is to remain is serviceable use during and following
construction. The incorporation of tiebacks or soil nails into the shoring system may not
be feasible on this site due to the close proximity of the property lines and the City of
Carlsbad right-of-way. If necessary, the use of internal braces and/or rakers may be used
to achieve the maximum shoring height needed to complete the recommended
excavations.
Shoring of excavations of this size is typically performed by specialty contractors with
knowledge of the City of Carlsbad ordinances, and current building codes, as well as the
local area soil conditions. Since the design of retaining systems is sensitive to surcharge
pressures behind the excavation, we recommend that this office be consulted if unusual
load conditions are uncovered in the placement/installation. To that end, GSI should
perform field reviews during shoring construction. Care should be exercised when
excavating into the on-site soils since caving or sloughing of the earth materials is possible.
Observation of soldier pile excavations and special inspections/testing should be
performed during shoring construction.
Shoring of the excavation is the responsibility of the shoring contractor. Extreme caution
should be used to reduce damage to any adjacent improvements caused by settlement
or reduction of lateral support. Accordingly, we recommend a system of surveying and
monitoring until the excavations are backfilled to the design grade in order to evaluate the
effects of shoring on existing onsite and offsite improvements. Pre-construction
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photo-documentation is also advisable. Unless incorporated into the shoring design,
construction equipment storage or traffic, and/or stockpiled soils/building materials should
not be stored or operated within ‘H’ feet of the top of any shored excavations (where ‘H’
equals the height of the retained earth). Temporary/permanent provisions should be made
to direct any potential runoff away from the top of shored excavations. All applicable
surcharges from vehicular traffic and existing structures within ‘H’ of a shored excavation
should be evaluated.
Lateral Pressure - Temporary Shoring
1.The active pressure to be utilized in the design of temporary shoring, retaining level
backfill conditions, may be computed by the triangular pressure distribution shown
in Figure 3.
2.Passive pressure may be computed as an equivalent fluid having a given density
shown in Figure 3.
3.The above criteria assumes that hydrostatic pressure is not allowed to build up
behind excavation walls.
4.Surcharge: These recommendations are for exposed excavation walls up to 10 feet
high. An empirical equivalent fluid pressure approach may be used to compute the
horizontal pressure against the wall. Appropriate fluid unit weights are provided for
specific slope gradients of the retained material; these do not include other
superimposed loading conditions such as traffic, structures, seismic events,
expansive soils or adverse geologic conditions. The traffic surcharge for light
passenger cars, trucks, and vans may be taken as 100 psf/ft in the upper 5 feet of
the wall. For heavy emergency vehicle or multi-axle (HS20) truck traffic, the traffic
surcharge should be 300 psf/ft in the upper 5 feet of the wall. This does not include
the surcharge of parked vehicles which should be evaluated at a higher surcharge
to account for the effects of seismic loading. It is not recommended to allow sloping
surcharge (other than level backfill) within “H” behind the shored walls from either
stockpiled soils or temporary/permanent graded slopes (where “H” equals the
height of the exposed shoring wall). Steeper slope gradients (more than level) will
increase the EFP for shoring design significantly as well as associated costs.
5.Deflection: The shoring system should be designed such that the maximum lateral
deformation at the top of the soldier pile not exceed 1 inch. The maximum lateral
deformation for the drilled pier concrete shafts at the lowest grade level should not
exceed ½ inch. The point of fixity, given a CIDH diameter of 18 to 24 inches and the
allowable deflection, should be on the order of 1 pile diameter from the depth of
excavation (dredge line) into unweathered formational deposits. Lateral deflection
may result in settlement of approximately ½ percent the total shoring height behind
the wall.
Figure 3
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6.Should a braced temporary shoring system be necessary, a maximum allowable
bearing of 2,000 psf may be used for a temporary concrete raker footing (deadman)
or by permanent lateral footings that are at least 12 inches wide by 12 inches below
the lowest adjacent grade (deep) into unweathered formational deposits. These
footings should be poured with the bearing surface normal to rakers inclined at
45 degrees. Alternatively, if a pile-supported raker is used, a passive pressure of
300 pcf may be used in the design of an 18-inch diameter cast-in-drilled hole (CIDH)
pile embedded into unweathered formational deposits. This value may be
increased by 20 percent for each additional foot of depth to a maximum lateral
bearing of 3,000 psf. The coefficient of friction between concrete and
Santiago Formation should be 0.35 when combined with the dead load forces.
Temporary Shoring Construction Recommendations
1.The excavation and installation of the soldier piles should be observed and
documented by the project geotechnical engineer to further evaluate the geologic
conditions within the influence of the temporary shoring wall and to ensure the
soldier pile construction conforms to the requirements of the shoring plan.
2.Drilled excavations for soldier piles should be straight and plumb. If boulders and
cobbles are encountered during drilling, the contractor should periodically recheck
the drilled shaft for plumbness.
3.Although not anticipated, casing should be provided in drilled shafts if perched
water and/or caving conditions are encountered during drilling operations. The
bottom of the casing should be at least 4 feet below the top of the concrete as the
concrete is poured and the casing is withdrawn. Although not anticipated,
dewatering may be required for concrete placement if significant seepage or
groundwater is encountered during construction. This should be considered during
project planning.
4.The exact tip elevation of the soldier piles should be clearly indicated on the shoring
plans.
5.All concrete should delivered through a tremie pipe immediately subsequent to
approved excavation and steel placement. Care should be taken to prevent striking
the walls of the excavations with the tremie pipe during concrete placement.
Concrete should not be allowed to free fall more than 5 feet. “Tailgating” concrete
will not be permitted.
6.Proper spacing (minimum of 3 inches) between H beams and the side walls, and
bottoms of the drilled shafts should be provided.
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7.Concrete used in the shoring construction should be tested by a qualified materials
testing consultant for strength and mix design.
8.Excavation for lagging should not commence until the soldier pile concrete reaches
its 28-day compressive strength.
9.A complete and accurate record of all soldier pile locations, depths, concrete,
strengths, quantity of concrete per pile should be maintained by the special
inspector and geotechnical consultant. The shoring design engineer should be
notified of any unusual conditions encountered during installation.
Monitoring of Shoring
1.The shoring designer or his designee should make periodic inspections of the job
site for the purpose of observing the installation of the shoring system and
monitoring of the survey.
2.Monitoring points should be established at the top of selected soldier piles and at
intermediate intervals as considered appropriate by the Geotechnical Engineer.
3.Control points should be established outside the area of influence of the shoring
system to ensure the accuracy of the monitoring readings.
4.Initial monitoring and photo-documentation should be performed prior to any
excavation.
5.Once the excavation has commenced, periodic readings should be taken weekly
until the excavation is backfilled to the design grade. If the performance of the
shoring system is within established guidelines, the shoring engineer may permit
the periodic readings to be bi-weekly. Permission to conduct bi-weekly readings
should be provided by the shoring design engineer in writing, and be distributed to
the Geotechnical Engineer-of-Record, Structural Engineer-of-Record, Civil
Engineer-of-Record, and shoring contractor. Once initiated, bi-weekly readings
should continue until the excavation is backfilled to the design grade. Thereafter,
readings can be made monthly. Additional readings should be taken when
requested by the special inspector, Shoring Design, Engineer, Structural
Engineer-of-Record, Geotechnical Engineer-of-Record, or the Building Official.
6.Monitoring reading should be submitted to the Shoring Design Engineer, and
Engineer in Responsible Charge, within three business days after they are
conducted. Monitoring readings should be accurate to within 0.01 feet. Results are
to be submitted in tabular form showing at least the initial date of monitoring and
reading, current monitoring date and reading and difference between the two
readings.
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7.If the total cumulative horizontal or vertical movement (from start of shoring
construction) of any nearby existing improvement reaches ½-inch or soldier piles
reaches 1 inch, all excavation activities should be suspended until the Geotechnical
Engineer and Shoring Design Engineer determine the cause of movement.
Supplemental shoring should be devised to eliminate further movement.
Supplemental shoring design will require review and approval by the Building
Official. Excavation should not re-commence until written permission is provided
by the Building Official.
Monitoring of Existing Improvements
1.The contractor should complete written and photographic logs of any existing
improvement located within 100 feet or three times the depth of shoring (whichever
is greater), prior to shoring construction. A licensed surveyor should document all
existing substantial cracks (i.e., greater than c inch horizontal or vertical separation)
in the existing structures/improvements.
2.The contractor should document the condition of the existing improvements
adjacent to the shoring wall prior to the start of shoring construction.
3.The contractor should monitor existing improvements for movement or cracking that
may result from the adjacent shoring.
4.If excessive movement or visible cracking occurs, the shoring contractor should
stop work and shore/reinforce the excavation, and contact the Shoring Design
Engineer and the Building Official.
5.Monitoring of the existing improvements should be made at reasonable intervals as
required by the registered design professional, subject to approval by the Building
Official. Monitoring should be performed by a licensed surveyor.
6.Prior to commencing shoring construction, a pre-construction meeting should take
place between the contractor, Shoring Design Engineer, Surveyor, and
Geotechnical Engineer, to identify monitoring locations on existing improvements.
7.If in the opinion of the Building Official or Shoring Design Engineer, monitoring data
indicate excessive movement or other distress, all excavation should cease until the
Geotechnical Engineer and Shoring Design Engineer investigates the situation and
makes recommendations for remedial actions or continuation.
8.All readings and measurements should be submitted to the Shoring Design
Engineer.
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WALLS/FENCES/IMPROVEMENTS
Perimeter Walls/Fences
Due to the potential for some settlement and tilting of the walls/fence within the unmitigated
zone and corresponding distress, should be expected. We recommend that the
walls/fences be constructed on deepened foundations utilizing a combination of grade
beam and drilled piers. The grade beam should be at a minimum of 12 inches by
12 inches in cross section, supported by drilled piers, 12 inches minimum in diameter,
placed at a maximum spacing of 6 feet on center, and with a minimum embedment length
of 5 feet into unweathered Santiago Formation. The strength of the concrete and grout
should be evaluated by the structural engineer of record. The proper ASTM tests for the
concrete and mortar should be provided along with the slump quantities. The concrete
used should be appropriate to mitigate sulfate corrosion, as warranted. The design of the
grade beam and caissons should be in accordance with the recommendations of the
project structural engineer, and include the utilization of the following geotechnical
parameters:
Point of Fixity:Located a distance of 1.5 times the pier’s diameter, below the
top of the unweathered Santiago Formation.
Passive Resistance:Passive earth pressure of 200 psf per foot of depth per foot of
caisson diameter, to a maximum value of 4,000 psf may be
used to determine pier depth and spacing, provided that they
meet or exceed the minimum requirements stated above. To
determine the total lateral resistance, the contribution of the
creep prone zone above the point of fixity, to passive
resistance, should be disregarded.
Allowable Axial Capacity:
Shaft capacity : 400 psf applied below the point of fixity over the surface area
of the shaft.
Tip capacity:4,000 psf.
DRIVEWAY, FLATWORK, AND OTHER IMPROVEMENTS
Some of the soil materials at the site are expansive. The effects of expansive soils are
cumulative, and typically occur over the lifetime of any improvements. On relatively level
areas, when the soils are allowed to dry, the dessication and swelling process tends to
cause heaving and distress to flatwork and other improvements. The resulting potential
for distress to improvements may be reduced, but not totally eliminated. To that end, all
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interested/affected parties should be informed of this long-term potential for distress. To
reduce the likelihood of distress, the following recommendations are presented for all
exterior flatwork:
1.The subgrade area for concrete slabs should be compacted to achieve a minimum
90 percent relative compaction, and then be presoaked to 2 to 3 percentage points
above (or 125 percent of) the soils’ optimum moisture content, to a depth of
18 inches below subgrade elevation. If very low expansive soils are present, only
optimum moisture content, or greater, is required and specific presoaking is not
warranted. The moisture content of the subgrade should be proof tested within
72 hours prior to pouring concrete. Mitigation of any potentially compressible soils
within the influence of the hardscape should be performed prior to subgrade
preparation.
2.Concrete slabs should be cast over a non-yielding surface, consisting of a 4-inch
layer of crushed rock, gravel, or clean sand, that should be compacted and level
prior to pouring concrete. If very low expansive soils are present, the rock or gravel
or sand may be deleted. The layer or subgrade should be wet-down completely
prior to pouring concrete, to minimize loss of concrete moisture to the surrounding
earth materials.
3.Exterior slabs should be a minimum of 4 inches thick. Driveway slabs and
approaches should additionally have a thickened edge (12 inches) adjacent to all
landscape areas, to help impede infiltration of landscape water under the slab.
4.The use of transverse and longitudinal control joints are recommended to help
control slab cracking due to concrete shrinkage or expansion. Two ways to
mitigate such cracking are: a) add a sufficient amount of reinforcing steel,
increasing tensile strength of the slab; and, b) provide an adequate amount of
control and/or expansion joints to accommodate anticipated concrete shrinkage
and expansion.
In order to reduce the potential for unsightly cracks, slabs should be reinforced at
mid-height with a minimum of No. 3 bars placed at 18 inches on center, in each
direction. If subgrade soils within the top 7 feet from finish grade are very low
expansive soils (i.e., E.I. #20), then 6x6-W1.4xW1.4 welded-wire mesh may be
substituted for the rebar, provided the reinforcement is placed on chairs, at slab
mid-height. The exterior slabs should be scored or saw cut, ½ to d inches deep,
often enough so that no section is greater than 10 feet by 10 feet. For sidewalks or
narrow slabs, control joints should be provided at intervals of every 6 feet. The
slabs should be separated from the foundations and sidewalks with expansion joint
filler material.
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5.No traffic should be allowed upon the newly poured concrete slabs until they have
been properly cured to within 75 percent of design strength. Concrete compression
strength should be a minimum of 2,500 psi.
6.Driveways, sidewalks, and patio slabs adjacent to the building should be separated
from this structure with thick expansion joint filler material. In areas directly adjacent
to a continuous source of moisture (i.e., irrigation, planters, etc.), all joints should
be additionally sealed with flexible mastic.
7.Planters and walls should not be tied to the building.
8.Overhang structures should be supported on the slabs, or structurally designed
with continuous footings tied in at least two directions. If very low expansion soils
are present, footings need only be tied in one direction.
9.Any masonry landscape walls that are to be constructed throughout the property
should be grouted and articulated in segments no more than 20 feet long. These
segments should be keyed or doweled together.
10.Utilities should be enclosed within a closed utilidor (vault) or designed with flexible
connections to accommodate differential settlement and expansive soil conditions.
11.Positive site drainage should be maintained at all times. Finish grade on the
property should provide a minimum of 1 to 2 percent fall to the street, as indicated
herein or conform to Section 1804.3 of the 2013 CBC (whichever is more
conservative). It should be kept in mind that drainage reversals could occur,
including post-construction settlement, if relatively flat yard drainage gradients are
not periodically maintained by the HOA.
12.Air conditioning (A/C) units should be supported by slabs that are incorporated into
the building foundation or constructed on a rigid slab with flexible couplings for
plumbing and electrical lines. A/C waste water lines should be drained to a suitable
non-erosive outlet.
13.Shrinkage cracks could become excessive if proper finishing and curing practices
are not followed. Finishing and curing practices should be performed per the
Portland Cement Association Guidelines. Mix design should incorporate rate of
curing for climate and time of year, sulfate content of soils, corrosion potential of
soils, and fertilizers used on site.
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PRELIMINARY PAVEMENT DESIGN/CONSTRUCTION
Structural Section
Traffic Index (TI) values were assumed to range between 4.5 and 5.0 for the private
roadway, and should be reviewed by the project civil engineer for comment, and any
revisions, as necessary. An R-value of 20 was assumed for preliminary planning purposes
in this study. The recommended preliminary pavement sections for both asphaltic
concrete (A.C.) pavement over aggregate base (A.B.) and Portland Cement Concrete
Pavement (P.C.C.P.) in the following tables:
APPROXIMATE
TRAFFIC AREA
TRAFFIC
INDEX(1)
SUBGRADE
R-VALUE(2)
A.C.
THICKNESS
(INCHES)
A.B.
THICKNESS(3)
(INCHES)
Private Street 4.5 20 4.0 4.0 (4)(4)
Private Street 5.0 20 4.0 6.0(4)
The TI is assumed based on the intended use and review of City of Carlsbad (2004). The TI should be(1)
reviewed revised as necessary by the project civil engineer. Trash disposal areas, entry areas, fire vehicle
access may require special design and/or detailing.
Estimate, to be verified during grading and prior to placement of the street section.(2)
Denotes Class 2 Aggregate Base R >78, SE >25).(3)
City minimum.(4)
PORTLAND CONCRETE CEMENT PAVEMENTS (PCCP)
TRAFFIC
AREAS
CONCRETE
TYPE
PCCP
THICKNESS
(INCHES)
TRAFFIC
AREAS
CONCRETE
TYPE
PCCP
THICKNESS
(INCHES)
Light Vehicles
520-C-2500 6.0
Heavy Truck Traffic
520-C-2500 8.0
560-C-3250 5.0 560-C-3250 7.0
NOTE: All PCCP is designed as un-reinforced and bearing directly on compacted subgrade. However, a
4-inch thick leveling course of compacted aggregate base, or crushed rock may be considered to improve
performance. All PCCP should be properly detailed (jointing, etc.) per the industry standard. Pavements
may be additionally reinforced with #4 reinforcing bars, placed 12 inches on center, each way, for improved
performance. Trash truck loading pads shall be 8 inches per the City standard and reinforced accordingly.
All pavement installation, including preparation and compaction of subgrade, compaction
of base material, and placement and rolling of asphaltic concrete, etc., shall be done in
accordance with the City of Carlsbad guidelines, and under the observation and testing of
the project geotechnical engineer and/or the City.
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The recommended pavement sections are meant as minimums. If thinner or highly
variable pavement sections are constructed, increased maintenance and repair may be
needed. The recommended pavement sections provided above are intended as a
minimum guideline. If thinner or highly variable pavement sections are constructed,
increased maintenance and repair could be expected. If the ADT (average daily traffic) or
ADTT (average daily truck traffic) increases beyond that intended, as reflected by the TI
used for design, increased maintenance and repair could be required for the pavement
section. Consideration should be given to the increased potential for distress from overuse
of paved street areas by heavy equipment and/or construction related heavy traffic
(e.g., concrete trucks, loaded supply trucks, etc.), particularly when the final section is not
in place (i.e., topcoat). Best management construction practices should be followed at all
times, especially during inclement weather.
PAVEMENT GRADING RECOMMENDATIONS
General
All section changes should be properly transitioned. If adverse conditions are encountered
during the preparation of subgrade materials, special construction methods may need to
be employed. A GSI representative should be present for the preparation of subgrade,
aggregate base, and asphaltic concrete.
Subgrade
Within street and parking areas, all surficial deposits of loose soil material should be
removed and recompacted as recommended. After the loose soils are removed, the
bottom is to be scarified to a depth of at least 6 inches, moisture conditioned as necessary
and compacted to 95 percent of the maximum laboratory density, as determined by
ASTM D 1557.
Deleterious material, excessively wet or dry pockets, concentrated zones of oversized rock
fragments, and any other unsuitable materials encountered during grading should be
removed. The compacted fill material should then be brought to the elevation of the
proposed subgrade for the pavement. The subgrade should be proof-rolled in order to
promote a uniform firm and unyielding surface. All grading and fill placement should be
observed by the project geotechnical consultant.
Aggregate Base
Compaction tests are required for the recommended aggregate base section. Minimum
relative compaction required will be 95 percent of the laboratory maximum density as
determined by ASTM D 1557. Base aggregate should be in accordance to the
“Greenbook” crushed aggregate base rock (minimum R-value=78).
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Paving
Prime coat may be omitted if all of the following conditions are met:
1.The asphalt pavement layer is placed within two weeks of completion of aggregate
base and/or sub base course.
2.Traffic is not routed over completed base before paving
3.Construction is completed during the dry season of May through October.
4.The aggregate base is kept free of debris prior to placement of asphaltic concrete.
If construction is performed during the wet season of November through April, prime coat
may be omitted if no rain occurs between completion of the aggregate base course and
paving and the time between completion of aggregate base and paving is reduced to three
days, provided the aggregate base is free of loose soil or debris. Where prime coat has
been omitted and rain occurs, traffic is routed over the aggregate base course, or paving
is delayed, measures shall be taken to restore the aggregate base course, and subgrade
to conditions that will meet specifications as directed by the geotechnical consultant. GSI
has assumed that traffic will not be allowed on recently placed AC for a period of 24 hours
or more.
Drainage
Positive drainage should be provided for all surface water to drain towards the area swale,
curb and gutter, or to an approved drainage channel. Positive site drainage should be
maintained at all times. Water should not be allowed to pond or seep into the ground,
such as from behind unprotected curbs, both during and after grading. If planters or
landscaping are adjacent to paved areas, measures should be taken to minimize the
potential for water to enter the pavement section, such as thickened edges, enclosed
planters, etc. Also, best management construction practices should be strictly adhered to
at all times to minimize the potential for distress during construction and roadway
improvements. Seismic effects may reverse relatively flat gradients in streets and gutters.
These should be periodically checked following a significant seismic event.
PCC Cross Gutters
PCC cross gutters should be designed in accordance with San Diego Regional Standard
Drawing (SDRSD) G-12.
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Additional Considerations
To mitigate perched groundwater, consideration should be given to installation of
subgrade separators (cut-offs) between pavement subgrade and landscape areas,
although this is not a requirement from a geotechnical standpoint. Cut-offs, if used, should
be 6 inches wide and at least 12 inches below the pavement subgrade contact or
12 inches below the crushed aggregate base rock, if utilized.
ONSITE INFILTRATION-RUNOFF RETENTION SYSTEMS
General
Onsite infiltration-runoff retention systems (OIRRS) are anticipated to be used for
Best Management Practices (BMP’s) or Low Impact Development (LID) principles for the
project. To that end, some guidelines should/must be followed in the planning, design,
and construction of such systems. Such facilities, if improperly designed or implemented
without consideration of the geotechnical aspects of site conditions, can contribute to
flooding, saturation of bearing materials beneath site improvements, slope instability, and
possible concentration and contribution of pollutants into the groundwater or storm drain
and/or utility trench systems.
A key factor in these systems is the infiltration rate (often referred to as the percolation rate)
which can be ascribed to, or determined for, the earth materials within which these
systems are installed. Additionally, the infiltration rate of the designed system (which may
include gravel, sand, mulch/topsoil, or other amendments, etc.) will need to be considered.
The project infiltration testing is very site specific, any changes to the location of the
proposed OIRRS and/or estimated size of the OIRRS, may require additional infiltration
testing.
Some of the methods which are utilized for onsite infiltration include percolation basins,
dry wells, bio-swale/bio-retention, permeable pavers/pavement, infiltration trenches, filter
boxes and subsurface infiltration galleries/chambers. Some of these systems are
constructed using native and import soils, perforated piping, and filter fabrics while others
employ structural components such as stormwater infiltration chambers and
filters/separators. Every site will have characteristics which should lend themselves to one
or more of these methods; but, not every site is suitable for OIRRS. In practice, OIRRS are
usually initially designed by the project design civil engineer. Selection of methods should
include (but should not be limited to) review by licensed professionals including the
geotechnical engineer, hydrogeologist, engineering geologist, project civil engineer,
landscape architect, environmental professional, and industrial hygienist. Applicable
governing agency requirements should be reviewed and included in design
considerations.
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The following geotechnical guidelines should be considered when designing onsite
infiltration-runoff retention systems:
•Based on our review of the United States Department of Agriculture (USDA) Soil
Survey, the onsite soils consist of the Diablo clay (15 to 30% slopes), the Las Flores
loamy fine sand (2 to 9% slopes), the Las Flores loamy fine sand (9 to 15% slopes),
and the Visalia sandy loam (2 to 5% slopes). The capacity of the most limiting layer
to transmit water (Ksat) for these soil units, and Hydrologic Soil Group (HSG) are
reported as:
Diablo clay (15 to 30 % slopes) - moderately low to moderately high (0.06 to
0.20 in/hr); and HSG classification as “D.”
Las Flores loamy fine sand (2 to 9% slopes) -very low to moderately low
(0.00 to 0.06 in/hr); and HSG classification as “D.”
Las Flores loamy fine sand (9 to 15 % slopes) -very low to moderately low
(0.00 to 0.06 in/hr); and HSG classification as “D.”
Visalia sandy loam (2 to 5% slopes) - High (1.98 to 5.95 in/hr); and HSG
Classification as “A.”
During our feasibility screening level investigation, GSI has evaluated the infiltration
rate of natural surface soils on the west site to be about 0.2 inches/hour, and on the
east site to be about 0.5 inches/hour (both conducted in USDA-mapped Hydrologic
Soil Group “A” areas). Prior development has resulted in the removal of natural
surface soils, and for all intent and purposes, the west site is predominantly a cut
lot exposing some surfical fill and dense sedimentary bedrock consisting of silty
sandstone, and significant fill thickness exist on the east site. On the east site,
artificial fill, created through removal/recompaction of onsite soils is of a similar, very
low permeability. The City of Carlsbad “Form I-8" is provided in Appendix F.
•Owing to the infiltration rate, and per the City of Carlsbad BMP Design Manual
(2016), infiltration for onsite storm water treatment is not recommended.
•It is not good engineering practice to allow water to saturate soils, especially near
slopes or improvements; however, the controlling agency/authority is now requiring
this for OIRRS purposes on many projects.
•If infiltration is planned, infiltration system design should be based on actual
infiltration testing results/data.
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•Wherever possible, infiltration systems should not be installed within ±50 feet of the
tops of slopes steeper than 15 percent or within H/3 from the tops of slopes (where
H equals the height of slope).
•Wherever possible, infiltrations systems should not be placed within a distance of
H/2 from the toes of slopes (where H equals the height of slope).
•Impermeable liners and subdrains should be used along the bottom of bioretention
swales/basins located within the influence of slopes or settlement sensitive
improvements. Impermeable liners used in conjunction with bioretention basins
should consist of a 30-mil polyvinyl chloride (PVC) membrane that is covered by a
minimum of 12 inches of clean soil, free from rocks and debris, with a maximum 4:1
(h:v) slope inclination, or flatter, and meets the following minimum specifications:
Specific Gravity (ASTM D792): 1.2 (g/cc, min.); Tensile (ASTM D882):
73 (lb/in-width, min); Elongation at Break (ASTM D882): 380 (%, min);
Modulus (ASTM D882): 30 (lb/in-width, min.); and Tear Strength
(ASTM D1004): 8 (lb/in, min); Seam Shear Strength (ASTM D882) 58.4 (lb/in,
min); Seam Peel Strength (ASTM D882) 15 (lb/in, min).
•Subdrains should consist of at least 4-inch diameter Schedule 40 or SDR 35 drain
pipe with perforations oriented down. The drain pipe should be sleeved with a filter
sock
•The landscape architect should be notified of the location of the proposed OIRRS.
If landscaping is proposed within the OIRRS, consideration should be given to the
type of vegetation chosen and their potential effect upon subsurface improvements
(i.e., some trees/shrubs will have an effect on subsurface improvements with their
extensive root systems). Over-watering landscape areas above, or adjacent to, the
proposed OIRRS could adversely affect performance of the system.
•Areas adjacent to, or within, the OIRRS that are subject to inundation should be
properly protected against scouring, undermining, and erosion, in accordance with
the recommendations of the design engineer.
•Seismic shaking may result in the formation of a seiche which could potential
overtop the banks of an OIRRS and result in down-gradient flooding and scour.
•If subsurface infiltration galleries/chambers are proposed, the appropriate size,
depth interval, and ultimate placement of the detention/infiltration system should be
evaluated by the design engineer, and be of sufficient width/depth to achieve
optimum performance, based on the infiltration rates provided. In addition, proper
debris filter systems will need to be utilized for the infiltration galleries/chambers.
Debris filter systems will need to be self cleaning and periodically and regularly
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maintained on a regular basis. Provisions for the regular and periodic maintenance
of any debris filter system is recommended and this condition should be disclosed
to all interested/affected parties.
•Infiltrations systems should not be installed within ±8 feet of building foundations
utility trenches, and walls, or a 1:1 (h:v) slope (down and away) from the bottom
elements of these improvements. Alternatively, deepened foundations and/or
pile/pier supported improvements may be used.
•Infiltrations systems should not be installed adjacent to pavement and/or hardscape
improvements. Alternatively, deepened/thickened edges and curbs and/or
impermeable liners may be utilized in areas adjoining the OIRRS.
•As with any OIRRS, localized ponding and groundwater seepage should be
anticipated. The potential for seepage and/or perched groundwater to occur after
site development should be disclosed to all interested/affected parties.
•Installation of infiltrations systems should avoid expansive soils (E.I. $51) or soils
with a relatively high plasticity index (P.I. > 20).
•Infiltration systems should not be installed where the vertical separation of the
groundwater level is less than ±10 feet from the base of the system.
•Where permeable pavements are planned as part of the system, the site Traffic
Index (T.I.) should be less than 25,000 Average Daily Traffic (ADT), as
recommended in Allen, et al. (2011).
•Infiltration systems should be designed using a suitable factor of safety (FOS) to
account for uncertainties in the known infiltration rates (as generally required by the
controlling authorities), and reduction in performance over time.
•As with any OIRRS, proper care will need to be provided. Best management
practices should be followed at all times, especially during inclement weather.
Provisions for the management of any siltation, debris within the OIRRS, and/or
overgrown vegetation (including root systems) should be considered. An
appropriate inspection schedule will need to adopted and provided to all
interested/affected parties.
•Any designed system will require regular and periodic maintenance, which may
include rehabilitation and/or complete replacement of the filter media (e.g., sand,
gravel, filter fabrics, topsoils, mulch, etc.) or other components utilized in
construction, so that the design life exceeds 15 years. Due to the potential for
piping and adverse seepage conditions, a burrowing rodent control program should
also be implemented onsite.
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•All or portions of these systems may be considered attractive nuisances. Thus,
consideration of the effects of, or potential for, vandalism should be addressed.
•Newly established vegetation/landscaping (including phreatophytes) may have root
systems that will influence the performance of the OIRRS or nearby LID systems.
•The potential for surface flooding, in the case of system blockage, should be
evaluated by the design engineer.
•Any proposed utility backfill materials (i.e., inlet/outlet piping and/or other
subsurface utilities) located within or near the proposed area of the OIRRS may
become saturated. This is due to the potential for piping, water migration, and/or
seepage along the utility trench line backfill. If utility trenches cross and/or are
proposed near the OIRRS, cut-off walls or other water barriers will need to be
installed to mitigate the potential for piping and excess water entering the utility
backfill materials. Planned or existing utilities may also be subject to piping of fines
into open-graded gravel backfill layers unless separated from overlying or adjoining
OIRRS by geotextiles and/or slurry backfill.
•The use of OIRRS above existing utilities that might degrade/corrode with the
introduction of water/seepage should be avoided.
•A vector control program may be necessary as stagnant water contained in OIRRS
may attract mammals, birds, and insects that carry pathogens.
DEVELOPMENT CRITERIA
Drainage
Adequate surface drainage is a very important factor in reducing the likelihood of adverse
performance of foundations, hardscape, and slopes. Surface drainage should be sufficient
to mitigate ponding of water anywhere on the property, and especially near structures and
tops of slopes. Surface drainage should be carefully taken into consideration during fine
grading, landscaping, and building construction. Therefore, care should be taken that
future landscaping or construction activities do not create adverse drainage conditions.
Positive site drainage within the property should be provided and maintained at all times.
Drainage should not flow uncontrolled down any descending slope. Water should be
directed away from foundations and tops of slopes, and not allowed to pond and/or seep
into the ground. In general, site drainage should conform to Section 1804.3 of the
2013 CBC. Consideration should be given to avoiding construction of planters adjacent
to the building. Building pad drainage should be directed toward the street or other
approved area(s). Although not a geotechnical requirement, roof gutters, down spouts,
or other appropriate means may be utilized to control roof drainage. Down spouts, or
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drainage devices should outlet a minimum of 5 feet from structures or into a subsurface
drainage system. Areas of seepage may develop due to irrigation or heavy rainfall, and
should be anticipated. Minimizing irrigation will lessen this potential. If areas of seepage
develop, recommendations for minimizing this effect could be provided upon request.
Erosion Control
Onsite earth materials have a moderate to high erosion potential. Consideration should
be given to providing hay bales and silt fences for the temporary control of surface water,
from a geotechnical viewpoint.
Landscape Maintenance
Only the amount of irrigation necessary to sustain plant life should be provided.
Over-watering the landscape areas will adversely affect proposed site improvements. We
would recommend that any proposed open-bottom planters adjacent to the structure be
eliminated for a minimum distance of 10 feet. As an alternative, closed-bottom type
planters could be utilized. An outlet placed in the bottom of the planter, could be installed
to direct drainage away from structures or any exterior concrete flatwork. If planters are
constructed adjacent to the structure, the sides and bottom of the planter should be
provided with a moisture barrier to prevent penetration of irrigation water into the
subgrade. Provisions should be made to drain the excess irrigation water from the planters
without saturating the subgrade below or adjacent to the planters. Consideration should
be given to the type of vegetation chosen and their potential effect upon surface
improvements (i.e., some trees will have an effect on concrete flatwork with their extensive
root systems). From a geotechnical standpoint leaching is not recommended for
establishing landscaping. If the surface soils are processed for the purpose of adding
amendments, they should be recompacted to 90 percent minimum relative compaction.
Gutters and Downspouts
As previously discussed in the drainage section, the installation of gutters and downspouts
should be considered to collect roof water that may otherwise infiltrate the soils adjacent
to the structures. If utilized, the downspouts should be drained into PVC collector pipes
or other non-erosive devices (e.g., paved swales or ditches; below grade, solid tight-lined
PVC pipes; etc.), that will carry the water away from the building, to an appropriate outlet,
in accordance with the recommendations of the design civil engineer. Downspouts and
gutters are not a requirement; however, from a geotechnical viewpoint, provided that
positive drainage is incorporated into project design (as discussed previously).
Subsurface and Surface Water
Subsurface and surface water are not anticipated to affect site development, provided that
the recommendations contained in this report are incorporated into final design and
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construction and that prudent surface and subsurface drainage practices are incorporated
into the construction plans. Perched groundwater conditions along zones of contrasting
permeabilities may not be precluded from occurring in the future due to site irrigation, poor
drainage conditions, or damaged utilities, and should be anticipated. Should perched
groundwater conditions develop, this office could assess the affected area(s) and provide
the appropriate recommendations to mitigate the observed groundwater conditions.
Groundwater conditions may change with the introduction of irrigation, rainfall, or other
factors.
Site Improvements
If in the future, any additional improvements (e.g., pools, spas, etc.) are planned for the
site, recommendations concerning the geological or geotechnical aspects of design and
construction of said improvements could be provided upon request. Pools and/or spas
should not be constructed without specific design and construction recommendations from
GSI, and this construction recommendation should be provided to all interested/affected
parties. This office should be notified in advance of any fill placement, grading of the site,
or trench backfilling after rough grading has been completed. This includes any grading,
utility trench and retaining wall backfills, flatwork, etc.
Tile Flooring
Tile flooring can crack, reflecting cracks in the concrete slab below the tile, although small
cracks in a conventional slab may not be significant. Therefore, the designer should
consider additional steel reinforcement for concrete slabs-on-grade where tile will be
placed. The tile installer should consider installation methods that reduce possible
cracking of the tile such as slipsheets. Slipsheets or a vinyl crack isolation membrane
(approved by the Tile Council of America/Ceramic Tile Institute) are recommended
between tile and concrete slabs on grade.
Additional Grading
This office should be notified in advance of any fill placement, supplemental regrading of
the site, or trench backfilling after rough grading has been completed. This includes
completion of grading in the street, driveway approaches, driveways, parking areas, and
utility trench and retaining wall backfills.
Footing Trench Excavation
All footing excavations should be observed by a representative of this firm subsequent to
trenching and prior to concrete form and reinforcement placement. The purpose of the
observations is to evaluate that the excavations have been made into the recommended
bearing material and to the minimum widths and depths recommended for construction.
If loose or compressible materials are exposed within the footing excavation, a deeper
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footing or removal and recompaction of the subgrade materials would be recommended
at that time. Footing trench spoil and any excess soils generated from utility trench
excavations should be compacted to a minimum relative compaction of 90 percent, if not
removed from the site.
Trenching/Temporary Construction Backcuts
Considering the nature of the onsite earth materials, it should be anticipated that caving
or sloughing could be a factor in subsurface excavations and trenching. Shoring or
excavating the trench walls/backcuts at the angle of repose (typically 25 to 45 degrees
[except as specifically superceded within the text of this report]), should be anticipated.
All excavations should be observed by an engineering geologist or soil engineer from GSI,
prior to workers entering the excavation or trench, and minimally conform to CAL-OSHA,
state, and local safety codes. Should adverse conditions exist, appropriate
recommendations would be offered at that time. The above recommendations should be
provided to any contractors and/or subcontractors, or homeowner(s), etc., that may
perform such work.
Utility Trench Backfill
1.All interior utility trench backfill should be brought to at least 2 percent above
optimum moisture content and then compacted to obtain a minimum relative
compaction of 90 percent of the laboratory standard. As an alternative for shallow
(12-inch to 18-inch) under-slab trenches, sand having a sand equivalent value of
30 or greater may be utilized and jetted or flooded into place. Observation, probing
and testing should be provided to evaluate the desired results.
2.Exterior trenches adjacent to, and within areas extending below a 1:1 plane
projected from the outside bottom edge of the footing, and all trenches beneath
hardscape features and in slopes, should be compacted to at least 90 percent of
the laboratory standard. Sand backfill, unless excavated from the trench, should
not be used in these backfill areas. Compaction testing and observations, along
with probing, should be accomplished to evaluate the desired results.
3.All trench excavations should conform to CAL-OSHA, state, and local safety codes.
4.Utilities crossing grade beams, perimeter beams, or footings should either pass
below the footing or grade beam utilizing a hardened collar or foam spacer, or pass
through the footing or grade beam in accordance with the recommendations of the
structural engineer.
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SUMMARY OF RECOMMENDATIONS REGARDING
GEOTECHNICAL OBSERVATION AND TESTING
We recommend that observation and/or testing be performed by GSI at each of the
following construction stages:
•During grading.
•During excavation.
•During placement of subdrains or other subdrainage devices, prior to placing fill
and/or backfill.
•After excavation of building footings, retaining wall footings, and free standing walls
footings, prior to the placement of reinforcing steel or concrete.
•Prior to pouring any slabs or flatwork, after presoaking/presaturation of building
pads and other flatwork subgrade, before the placement of concrete, reinforcing
steel, capillary break (i.e., sand, pea-gravel, etc.), or vapor retarders (i.e., visqueen,
etc.).
•During retaining wall subdrain installation, prior to backfill placement.
•During placement of backfill for area drain, interior plumbing, utility line trenches,
and retaining wall backfill.
•During any slope construction/repair.
•When any unusual soil conditions are encountered during any construction
operations, subsequent to the issuance of this report.
•When any homeowner improvements, such as flatwork, spas, pools, walls, etc., are
constructed, prior to construction.
•A report of geotechnical observation and testing should be provided at the
conclusion of each of the above stages, in order to provide concise and clear
documentation of site work, and/or to comply with code requirements.
OTHER DESIGN PROFESSIONALS/CONSULTANTS
The design civil engineer, structural engineer, post-tension designer, architect, landscape
architect, wall designer, etc., should review the recommendations provided herein,
incorporate those recommendations into all their respective plans, and by explicit
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reference, make this report part of their project plans. This report presents minimum
design criteria for the design of slabs, foundations and other elements possibly applicable
to the project. These criteria should not be considered as substitutes for actual designs
by the structural engineer/designer. Please note that the recommendations contained
herein are not intended to preclude the transmission of water or vapor through the slab or
foundation. The structural engineer/foundation and/or slab designer should provide
recommendations to not allow water or vapor to enter into the structure so as to cause
damage to another building component, or so as to limit the installation of the type of
flooring materials typically used for the particular application.
The structural engineer/designer should analyze actual soil-structure interaction and
consider, as needed, bearing, expansive soil influence, and strength, stiffness and
deflections in the various slab, foundation, and other elements in order to develop
appropriate, design-specific details. As conditions dictate, it is possible that other
influences will also have to be considered. The structural engineer/designer should
consider all applicable codes and authoritative sources where needed. If analyses by the
structural engineer/designer result in less critical details than are provided herein as
minimums, the minimums presented herein should be adopted. It is considered likely that
some, more restrictive details will be required.
If the structural engineer/designer has any questions or requires further assistance, they
should not hesitate to call or otherwise transmit their requests to GSI. In order to mitigate
potential distress, the foundation and/or improvement’s designer should confirm to GSI
and the governing agency, in writing, that the proposed foundations and/or improvements
can tolerate the amount of differential settlement and/or expansion characteristics and
other design criteria specified herein.
PLAN REVIEW
Final project plans (grading, precise grading, foundation, retaining wall, landscaping, etc.),
should be reviewed by this office prior to construction, so that construction is in
accordance with the conclusions and recommendations of this report. Based on our
review, supplemental recommendations and/or further geotechnical studies may be
warranted.
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LIMITATIONS
The materials encountered on the project site and utilized for our analysis are believed
representative of the area; however, soil and bedrock materials vary in character between
excavations and natural outcrops or conditions exposed during mass grading. Site
conditions may vary due to seasonal changes or other factors.
Inasmuch as our study is based upon our review and engineering analyses and laboratory
data, the conclusions and recommendations are professional opinions. These opinions
have been derived in accordance with current standards of practice, and no warranty,
either express or implied, is given. Standards of practice are subject to change with time.
GSI assumes no responsibility or liability for work or testing performed by others, or their
inaction; or work performed when GSI is not requested to be onsite, to evaluate if our
recommendations have been properly implemented. Use of this report constitutes an
agreement and consent by the user to all the limitations outlined above, notwithstanding
any other agreements that may be in place. In addition, this report may be subject to
review by the controlling authorities. Thus, this report brings to completion our scope of
services for this portion of the project. All samples will be disposed of after 30 days, unless
specifically requested by the client, in writing.
GeoSoils, Inc.
APPENDIX A
REFERENCES
GeoSoils, Inc.
APPENDIX A
REFERENCES
American Concrete Institute, Committee 318, 2011, Building code requirements for
structural concrete (ACI318-11) and commentary, dated August.
American Concrete Institute (ACI) Committee 302, 2004, Guide for concrete floor and slab
construction, ACI 302.1R-04, dated June.
Allen, V., Connerton, A., and Carlson, C., 2011, Introduction to Infiltration Best
Management Practices (BMP), Contech Construction Products, Inc., Professional
Development Series, dated December.
American Society for Testing and Materials (ASTM), 2003, Standard test method for
infiltration rate of soils in field using double-ring infiltrometer, Designation
D 3385-03, dated August.
_____,1998, Standard practice for installation of water vapor retarder used in contact with
earth or granular fill under concrete slabs, Designation: E 1643-98 (Reapproved
2005).
_____, 1997, Standard specification for plastic water vapor retarders used in contact with
soil or granular fill under concrete slabs, Designation: E 1745-97 (Reapproved
2004).
American Society of Civil Engineers, 2010, Minimum design loads for buildings and other
structures, ASCE Standard ASCE/SEI 7-10.
Blake, Thomas F., 2000a, EQFAULT, A computer program for the estimation of peak
horizontal acceleration from 3-D fault sources; Windows 95/98 version.
_____, 2000b, EQSEARCH, A computer program for the estimation of peak horizontal
acceleration from California historical earthquake catalogs; Updated to January
2015, Windows 95/98 version.
Bozorgnia, Y., Campbell K.W., and Niazi, M., 1999, Vertical ground motion: Characteristics,
relationship with horizontal component, and building-code implications;
Proceedings of the SMIP99 seminar on utilization of strong-motion data,
September 15, Oakland, pp. 23-49.
Bryant, W.A., and Hart, E.W., 2007, Fault-rupture hazard zones in California, Alquist-Priolo
earthquake fault zoning act with index to earthquake fault zones maps;
California Geological Survey, Special Publication 42, interim revision.
GeoSoils, Inc.Summerhill Homes Appendix A
File:e:\wp12\7000\7103a.pge Page 2
California Building Standards Commission, 2013, California Building Code, California Code
of Regulations, Title 24, Part 2, Volume 2 of 2, Based on the 2012 International
Building Code, 2013 California Historical Building Code, Title 24, Part 8; 2013
California Existing Building Code, Title 24, Part 10.
California Department of Conservation, California Geological Survey (CGS), 2008,
Guidelines for evaluating and mitigating seismic hazards in California: California
Geological Survey Special Publication 117A (revised 2008), 102 p.
Cao, T., Bryant, W.A., Rowshandel, B., Branum, D., and Wills, C.J., 2003, The revised 2002
California probabilistic seismic hazard maps, dated June,
http://www.conservation.ca.gov/cgs/rghm/psha/fault_parameters/pdf/Documents
/2002_CA_Hazard_Maps.pdf
City of Carlsbad, 1992, Geotechnical Hazards analysis and mapping Study, November.
Jennings, C.W., and Bryant, W.A., 2010, Fault activity map of California, scale 1:750,000,
California Geological Survey, Geologic Data Map No. 6.
Kanare, H.M., 2005, Concrete floors and moisture, Engineering Bulletin 119, Portland
Cement Association.
Kennedy, MP., and Tan, SS., 2007, Geologic map of the Oceanside 30' by 60' quadrangle,
California, regional geologic map series, scale 1:100,000, California Geologic
Survey Map No. 2.
_____, 2005, Geologic map of the Oceanside 30' by 60' quadrangle, California, regional
map series, scale 1:100,000, California Geologic Survey and United States
Geological Survey, www.conservation.ca.gov/cgs/rghm/
rgm/preliminary_geologic_maps.htm
KTGY Architecture + Planning, 2016, Aviara Apartments, Capacity study - Options 1, 2 & 3,
three sheets, job # 20160328, dated May 12, May 4, and May 4, respectively
Norris, R.M. and Webb, R.W., 1990, Geology of California, second edition, John Wiley &
Sons, Inc.
REC Consultants, Inc., 2016, Site exhibit, 6145 Laurel Tree Toad, Carslbad, CA., plot date
June 22.
Robert Prater Associates, 2000, Earthwork observation, testing, and as-built geology
services, Kelly Ranch corporate center-building pads 2A, 2B, and 3, Carlsbad,
California, project no. 543-!B, 00-110, dated April 12.
GeoSoils, Inc.Summerhill Homes Appendix A
File:e:\wp12\7000\7103a.pge Page 3
_____, 1997, Geotechnical investigation, Kelly Ranch corporate center, Carlsbad,
California, project no. 543-1A. 97-145, dated April 30.
Robert Prater Associates, 1997, Geotechnical investigation for Kelly Ranch Corporate
Center, job no. 543-1A, 97-145, dated April 30
Romanoff, M., 1957, Underground corrosion, originally issued April 1.
Seed, 2005, Evaluation and mitigation of soil liquefaction hazard “evaluation of field data
and procedures for evaluating the risk of triggering (or inception) of liquefaction,”
in Geotechnical earthquake engineering; short course, San Diego, California,
April 8-9.
Sowers and Sowers, 1979, Unified soil classification system (After U. S. Waterways
Experiment Station and ASTM 02487-667) in Introductory Soil Mechanics,
New York.
State of California, 2016, Civil Code, Sections 895 et seq.
State of California Department of Transportation, Division of Engineering Services,
Materials Engineering, and Testing Services, Corrosion Technology Branch, 2003,
Corrosion Guidelines, Version 1.0, dated September.
Tan, S.S. and Giffen, D.G., 1995, Landslide hazards in the northern part of the San Diego
metropolitan area, San Diego County, California, DMG open file report 95-04,
landslide hazard identification map no. 35, relative landslide susceptibility and
landslide distribution map, plate G, 1:24,000 scale.
U.S. Geological Survey, 2013, U.S. Seismic Design Maps, Earthquake Hazards Program,
http://geohazards.usgs.gov/designmaps/us/application.php, version 3.1.0.
GeoSoils, Inc.
APPENDIX B
BORING LOGS AND CPT SOUNDINGS
UNIFIED SOIL CLASSIFICATION SYSTEM CONSISTENCY OR RELATIVE DENSITY
Major Divisions Group
Symbols Typical Names CRITERIA
Coarse-Grained SoilsMore than 50% retained on No. 200 sieveGravels 50% or more of coarse fraction retained on No. 4 sieveCleanGravelsGW Well-graded gravels and gravel-sand mixtures, little or no fines Standard Penetration Test
Penetration
Resistance N Relative (blows/ft) Density
0 - 4 Very loose
4 - 10 Loose
10 - 30 Medium
30 - 50 Dense
> 50 Very dense
GP
Poorly graded gravels and
gravel-sand mixtures, little or no
fines
GravelwithGM Silty gravels gravel-sand-silt
mixtures
GC Clayey gravels, gravel-sand-clay
mixtures
Sands more than 50% ofcoarse fractionpasses No. 4 sieveCleanSandsSW Well-graded sands and gravelly
sands, little or no fines
SP Poorly graded sands andgravelly sands, little or no fines
SandswithFinesSM Silty sands, sand-silt mixtures
SC Clayey sands, sand-clay
mixtures
Fine-Grained Soils50% or more passes No. 200 sieveSilts and ClaysLiquid limit50% or lessML Inorganic silts, very fine sands,rock flour, silty or clayey finesands
Standard Penetration Test
Unconfined
Penetration Compressive
Resistance N Strength
(blows/ft) Consistency (tons/ft
2)
<2 Very Soft <0.25
2 - 4 Soft 0.25 - .050
4 - 8 Medium 0.50 - 1.00
8 - 15 Stiff 1.00 - 2.00
15 - 30 Very Stiff 2.00 - 4.00
>30 Hard >4.00
CL
Inorganic clays of low to
medium plasticity, gravelly clays,
sandy clays, silty clays, lean
clays
OL Organic silts and organic silty
clays of low plasticity
Silts and ClaysLiquid limitgreater than 50%MH
Inorganic silts, micaceous or
diatomaceous fine sands or silts,
elastic silts
CH Inorganic clays of high plasticity,
fat clays
OH Organic clays of medium to high
plasticity
Highly Organic Soils PT
Peat, mucic, and other highly
organic soils
3" 3/4" #4 #10 #40 #200 U.S. Standard Sieve
Unified Soil
Classification Cobbles Gravel Sand Silt or Clay
coarse fine coarse medium fine
MOISTURE CONDITIONS MATERIAL QUANTITY OTHER SYMBOLS
Dry Absence of moisture: dusty, dry to the touch trace 0 - 5 % C Core Sample
Slightly Moist Below optimum moisture content for compaction few 5 - 10 % S SPT Sample
Moist Near optimum moisture content little 10 - 25 % B Bulk Sample
Very Moist Above optimum moisture content some 25 - 45 % – Groundwater
Wet Visible free water; below water table Qp Pocket Penetrometer
BASIC LOG FORMAT:
Group name, Group symbol, (grain size), color, moisture, consistency or relative density. Additional comments: odor, presence of roots, mica, gypsum,
coarse grained particles, etc.
EXAMPLE:
Sand (SP), fine to medium grained, brown, moist, loose, trace silt, little fine gravel, few cobbles up to 4" in size, some hair roots and rootlets.
File:Mgr: c;\SoilClassif.wpd PLATE B-1
ML
CL
CL
CL
SM
26
31
9
29
11
22
20
103.2
114.7
98.3
6.8
8.0
17.8
13.1
32.1
24.1
18.7
78.5
93.6
UNDOCUMENTED FILL:
@ 0' SANDY SILT, reddish yellow to light brown, dry, medium
dense; broken rock/concrete encountered, oxidation staining,
fine grained.
@ 3' SANDY CLAY, yellowish brown, damp, medium stiff; fine
grained.
@ 9' As per 3', moist, stiff; traces of gravel and asphalt
fragments.
ALLUVIUM:
@ 13' SANDY CLAY, dark reddish brown, very moist, stiff; fine
grained, small pebbles encountered.
SANTIAGO FORMATION:
@ 17' CLAYSTONE, light yellow brown to yellowish gray, very
moist to wet, stiff.
@ 21½' Groundwater encountered.
@ 23' SILTY SANDSTONE with trace CLAY, yellowish brown,
wet to saturated, loose to medium dense; fine grained.
@ 29' As per 17', light gray, wet, medium stiff.
7103-A-SC
Groundwater
USCS SymbolPROJECT:
7103-A-SC
Sample
DATE EXCAVATED
BORING LOG
Seepage
Blows/Ft.1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
Hollow Stem Auger
Dry Unit Wt. (pcf)B-1
Saturation (%)W.O.
PLATE
6-15-16
BulkStandard Penetration Test
Undisturbed, Ring Sample
2
Depth (ft.)Approx. Elevation: 104' MSL
Laurel Tree Lane At College Boulevard, Carslbad
SHEET OF1BORING
Description of Material
Laurel Tree Lane At College Boulevard, Carslbad
GeoSoils, Inc.
GeoSoils, Inc.
SUMMERHILL HOMES
SAMPLE METHOD:UndisturbedMoisture (%)B-2
SM
30
42
46
22
94.2
97.5
29.7
28.8
29.4
24.9
100
100
@ 35' SILTY SANDSTONE, yellowish brown, saturated,
medium dense; mottled, signs of oxidation.
@ 40' As per 35'.
@ 45' As per 35', trace CLAY.
@ 49' SILTY SANDSTONE with trace CLAY, light gray brown,
saturated, medium dense; interbeds of oxidized clay.
Total Depth = 50'
No Caving Encountered
Groundwater Encountered @ 21½'
Backfilled 6-15-2016 Per DEH Requirements
7103-A-SC
Groundwater
USCS SymbolPROJECT:
7103-A-SC
Sample
DATE EXCAVATED
BORING LOG
Seepage
Blows/Ft.31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
Hollow Stem Auger
Dry Unit Wt. (pcf)B-1
Saturation (%)W.O.
PLATE
6-15-16
BulkStandard Penetration Test
Undisturbed, Ring Sample
2
Depth (ft.)Approx. Elevation: 104' MSL
Laurel Tree Lane At College Boulevard, Carslbad
SHEET OF2BORING
Description of Material
Laurel Tree Lane At College Boulevard, Carslbad
GeoSoils, Inc.
GeoSoils, Inc.
SUMMERHILL HOMES
SAMPLE METHOD:UndisturbedMoisture (%)B-3
GeoSoils, Inc.
GeoSoils, Inc.
SUMMERHILL HOMES
SAMPLE METHOD:UndisturbedMoisture (%)B-4
CL
SM
SM
35
27/
50-5"
50-5"
31/
50-6"
50-6"
40/
50-4"
50-3"
116.0
113.7
102.7
115.0
12.5
15.5
14.0
14.1
16.1
13.1
13.2
77.8
81.7
69.6
80.0
UNDOCUMENTED FILL:
@ 0' SANDY CLAY with SILT inclusions, light yellow brown to
light gray, moist, medium stiff.
WEATHERED SANTIAGO FORMATION:
@ 3' SILTY SANDSTONE, dark reddish brown, moist, very
dense; fine grained.
SANTIAGO FORMATION:
@ 9½' SILTY SANDSTONE, light gray, damp to moist, dense;
thinly bedded.
@ 14' SILTY SANDSTONE, light gray to dark red, damp, very
dense; fine grained.
@ 19' SILTY SANDSTONE, light gray, moist, dense; fine
grained, thinly bedded.
@ 23½' As per 19', dark red hues, wet, very dense.
@ 29' As per 23½', dusky red.
7103-A-SC
Groundwater
USCS SymbolPROJECT:
7103-A-SC
Sample
DATE EXCAVATED
BORING LOG
Seepage
Blows/Ft.1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
Hollow Stem Auger
Dry Unit Wt. (pcf)B-2
Saturation (%)W.O.
PLATE
6-15-16
BulkStandard Penetration Test
Undisturbed, Ring Sample
2
Depth (ft.)Approx. Elevation: 82' MSL
Laurel Tree Lane At College Boulevard, Carslbad
SHEET OF1BORING
Description of Material
Laurel Tree Lane At College Boulevard, Carslbad
7103-A-SC
Groundwater
USCS SymbolPROJECT:
7103-A-SC
Sample
DATE EXCAVATED
BORING LOG
Seepage
Blows/Ft.31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
Hollow Stem Auger
Dry Unit Wt. (pcf)B-2
Saturation (%)W.O.
PLATE
6-15-16
BulkStandard Penetration Test
Undisturbed, Ring Sample
2
Depth (ft.)Approx. Elevation: 82' MSL
Laurel Tree Lane At College Boulevard, Carslbad
SHEET OF2BORING
Description of Material
SM
50-5½"
50-2½"99.6
15.5
24.6 98.5
@ 33½' As per 29', brownish yellow; weathered.
@ 37' Water added for ease of boring material.
@ 39' As per 33½', wet due to water addition.
Practical Refusal @ 40'
No Groundwater/Caving Encountered
Backfilled 6-15-2016 Per DEH Requirements
Laurel Tree Lane At College Boulevard, Carslbad
GeoSoils, Inc.
GeoSoils, Inc.
SUMMERHILL HOMES
SAMPLE METHOD:UndisturbedMoisture (%)B-5
GeosoilsProjectSummerhill Homes OperatorDG-RCFilenameSDF(568).cptJob Number7103-A-SCCone NumberDDG1366GPSHole NumberCPT-01Date and Time6/17/2016 7:50:19 AMMaximum Depth50.52 ftEST GW Depth During Test17.20 ftNet Area Ratio .8Cone Size 10cm squaredSoil Behavior Referance*Soil behavior type and SPT based on data from UBC-1983 0 5 10 15 20 25 30 35 40 45 50 0 500 TIPTSF 0 10 FRICTIONTSF 0 8 Fs/Qt% 0 200 SPT N0121 - sensitive fine grained 2 - organic material 3 - clay 4 - silty clay to clay 5 - clayey silt to silty clay 6 - sandy silt to clayey silt 7 - silty sand to sandy silt 8 - sand to silty sand 9 - sand 10 - gravelly sand to sand 11 - very stiff fine grained (*)12 - sand to clayey sand (*) CPT DATADEPTH(ft)SOILBEHAVIORTYPE
GeosoilsDepth 4.92ftRef*Arrival 9.61mSVelocity*Depth 10.01ftRef 4.92ftArrival 15.16mSVelocity 712.30ft/SDepth 14.93ftRef 10.01ftArrival 21.40mSVelocity 711.15ft/SDepth 20.01ftRef 14.93ftArrival 28.90mSVelocity 642.55ft/SDepth 24.93ftRef 20.01ftArrival 34.69mSVelocity 823.70ft/SDepth 30.02ftRef 24.93ftArrival 40.78mSVelocity 816.22ft/SDepth 35.10ftRef 30.02ftArrival 46.40mSVelocity 889.86ft/SDepth 40.03ftRef 35.10ftArrival 51.87mSVelocity 889.24ft/SDepth 44.95ftRef 40.03ftArrival 57.50mSVelocity 866.79ft/S 0 10 20 30 40 50 60 70 80 90 100 Depth 50.20ftRef 44.95ftArrival 63.28mSVelocity 901.28ft/STime (mS)Hammer to Rod String Distance (ft): 5.83* = Not DeterminedGPS DATA: ,,CPT-01Summerhill Homes
GeosoilsProjectSummerhill HomesOperatorDG-RCFilenameSDF(569).cptJob Number7103-A-SCCone NumberDDG1366GPSHole NumberCPT-03Date and Time6/17/2016 8:48:57 AMMaximum Depth50.52 ftEST GW Depth During Test17.00 ftNet Area Ratio .8Cone Size 10cm squaredSoil Behavior Referance*Soil behavior type and SPT based on data from UBC-1983 0 5 10 15 20 25 30 35 40 45 50 0 500 TIPTSF 0 10 FRICTIONTSF 0 8 Fs/Qt% 0 200 SPT N0121 - sensitive fine grained 2 - organic material 3 - clay 4 - silty clay to clay 5 - clayey silt to silty clay 6 - sandy silt to clayey silt 7 - silty sand to sandy silt 8 - sand to silty sand 9 - sand 10 - gravelly sand to sand 11 - very stiff fine grained (*)12 - sand to clayey sand (*) CPT DATADEPTH(ft)SOILBEHAVIORTYPE
GeosoilsDepth 4.92ftRef*Arrival 6.72mSVelocity*Depth 10.01ftRef 4.92ftArrival 14.76mSVelocity 491.00ft/SDepth 14.93ftRef 10.01ftArrival 20.00mSVelocity 849.13ft/SDepth 20.01ftRef 14.93ftArrival 25.47mSVelocity 881.22ft/SDepth 24.93ftRef 20.01ftArrival 30.78mSVelocity 896.38ft/SDepth 30.02ftRef 24.93ftArrival 36.33mSVelocity 896.70ft/SDepth 34.94ftRef 30.02ftArrival 42.65mSVelocity 765.42ft/SDepth 40.03ftRef 34.94ftArrival 47.97mSVelocity 945.86ft/SDepth 44.95ftRef 40.03ftArrival 53.75mSVelocity 843.36ft/S 0 10 20 30 40 50 60 70 80 90 100 Depth 50.03ftRef 44.95ftArrival 59.21mSVelocity 922.99ft/STime (mS)Hammer to Rod String Distance (ft): 5.83* = Not DeterminedGPS DATA: ,,CPT-03Summerhill Homes
GeosoilsLocationSummerhill HomesOperatorDG-RCJob Number7103-A-SCCone NumberDDG1366GPSHole NumberCPT-03Date and Time6/17/2016 8:48:57 AMEquilized Pressure 2.9EST GW Depth During Test17.224.11 ft 0Time (Sec)1400.0030PRESSURE U2 PSIPage 1 of 1
GeosoilsProjectSummerhill HomesOperatorDG-RCFilenameSDF(571).cptJob Number7103-A-SCCone NumberDDG1366GPSHole NumberCPT-04ADate and Time6/17/2016 10:25:25 AMMaximum Depth6.73 ftEST GW Depth During Test17.00 ftNet Area Ratio .8Cone Size 10cm squaredSoil Behavior Referance*Soil behavior type and SPT based on data from UBC-1983 0 5 10 15 20 25 30 35 40 45 50 0 500 TIPTSF 0 10 FRICTIONTSF 0 8 Fs/Qt% 0 200 SPT N0121 - sensitive fine grained 2 - organic material 3 - clay 4 - silty clay to clay 5 - clayey silt to silty clay 6 - sandy silt to clayey silt 7 - silty sand to sandy silt 8 - sand to silty sand 9 - sand 10 - gravelly sand to sand 11 - very stiff fine grained (*)12 - sand to clayey sand (*) CPT DATADEPTH(ft)SOILBEHAVIORTYPE
GeosoilsProjectSummerhill HomesOperatorDG-RCFilenameSDF(572).cptJob Number7103-A-SCCone NumberDDG1366GPSHole NumberCPT-06Date and Time6/17/2016 11:06:35 AMMaximum Depth42.49 ftEST GW Depth During Test17.00 ftNet Area Ratio .8Cone Size 10cm squaredSoil Behavior Referance*Soil behavior type and SPT based on data from UBC-1983 0 5 10 15 20 25 30 35 40 45 50 0 500 TIPTSF 0 10 FRICTIONTSF 0 8 Fs/Qt% 0 200 SPT N0121 - sensitive fine grained 2 - organic material 3 - clay 4 - silty clay to clay 5 - clayey silt to silty clay 6 - sandy silt to clayey silt 7 - silty sand to sandy silt 8 - sand to silty sand 9 - sand 10 - gravelly sand to sand 11 - very stiff fine grained (*)12 - sand to clayey sand (*) CPT DATADEPTH(ft)SOILBEHAVIORTYPE
GeosoilsDepth 4.92ftRef*Arrival 10.47mSVelocity*Depth 10.01ftRef 4.92ftArrival 15.70mSVelocity 754.82ft/SDepth 14.93ftRef 10.01ftArrival 20.31mSVelocity 964.27ft/SDepth 20.01ftRef 14.93ftArrival 24.61mSVelocity 1121.55ft/SDepth 25.10ftRef 20.01ftArrival 29.22mSVelocity 1067.78ft/SDepth 30.02ftRef 25.10ftArrival 33.83mSVelocity 1044.42ft/SDepth 34.94ftRef 30.02ftArrival 38.51mSVelocity 1033.31ft/SDepth 40.03ftRef 34.94ftArrival 43.67mSVelocity 974.52ft/S 0 10 20 30 40 50 60 70 80 90 100 Depth 42.49ftRef 40.03ftArrival 45.54mSVelocity 1299.48ft/STime (mS)Hammer to Rod String Distance (ft): 5.83* = Not DeterminedGPS DATA: ,,CPT-06Summerhill Homes
GeoSoils, Inc.
APPENDIX C
SEISMICITY
SITE
-100
0
100
200
300
400
500
600
700
800
900
1000
1100
-400 -300 -200 -100 0 100 200 300 400 500 600
CALIFORNIA FAULT MAP
SUMMERHILL
W.O. 7103-A-SC
PLATE C-1
7103-EQF
***********************
* *
* E Q F A U L T *
* *
* Version 3.00 *
* *
***********************
DETERMINISTIC ESTIMATION OF
PEAK ACCELERATION FROM DIGITIZED FAULTS
JOB NUMBER: 7103-A-SC
DATE: 06-29-2016
JOB NAME: SUMMERHILL
CALCULATION NAME: 7103 EQF
FAULT-DATA-FILE NAME: C:\Program Files\EQFAULT1\CDMGFLTE.DAT
SITE COORDINATES:
SITE LATITUDE: 33.1220
SITE LONGITUDE: 117.3020
SEARCH RADIUS: 62.4 mi
ATTENUATION RELATION: 11) Bozorgnia Campbell Niazi (1999) Hor.-Pleist. Soil-Cor.
UNCERTAINTY (M=Median, S=Sigma): S Number of Sigmas: 1.0
DISTANCE MEASURE: cdist
SCOND: 1
Basement Depth: .01 km Campbell SSR: 0 Campbell SHR: 0
COMPUTE PEAK HORIZONTAL ACCELERATION
FAULT-DATA FILE USED: C:\Program Files\EQFAULT1\CDMGFLTE.DAT
MINIMUM DEPTH VALUE (km): 3.0
Page 1
W.O. 7103-A-SC
PLATE C-2
7103-EQF
---------------
EQFAULT SUMMARY
---------------
-----------------------------
DETERMINISTIC SITE PARAMETERS
-----------------------------
Page 1
-------------------------------------------------------------------------------
| |ESTIMATED MAX. EARTHQUAKE EVENT
| APPROXIMATE |-------------------------------
ABBREVIATED | DISTANCE | MAXIMUM | PEAK |EST. SITE
FAULT NAME | mi (km) |EARTHQUAKE| SITE |INTENSITY
| | MAG.(Mw) | ACCEL. g |MOD.MERC.
================================|==============|==========|==========|=========
ROSE CANYON | 5.3( 8.6)| 6.9 | 0.552 | X
NEWPORT-INGLEWOOD (Offshore) | 8.0( 12.8)| 6.9 | 0.420 | X
CORONADO BANK | 21.0( 33.8)| 7.4 | 0.240 | IX
ELSINORE-TEMECULA | 24.4( 39.2)| 6.8 | 0.139 | VIII
ELSINORE-JULIAN | 24.4( 39.2)| 7.1 | 0.170 | VIII
ELSINORE-GLEN IVY | 36.2( 58.2)| 6.8 | 0.092 | VII
PALOS VERDES | 38.5( 62.0)| 7.1 | 0.106 | VII
EARTHQUAKE VALLEY | 41.9( 67.5)| 6.5 | 0.064 | VI
SAN JACINTO-ANZA | 47.2( 75.9)| 7.2 | 0.092 | VII
SAN JACINTO-SAN JACINTO VALLEY | 48.2( 77.6)| 6.9 | 0.073 | VII
NEWPORT-INGLEWOOD (L.A.Basin) | 49.2( 79.2)| 6.9 | 0.071 | VI
CHINO-CENTRAL AVE. (Elsinore) | 50.6( 81.5)| 6.7 | 0.085 | VII
SAN JACINTO-COYOTE CREEK | 51.4( 82.8)| 6.8 | 0.064 | VI
WHITTIER | 54.2( 87.2)| 6.8 | 0.060 | VI
ELSINORE-COYOTE MOUNTAIN | 55.5( 89.3)| 6.8 | 0.059 | VI
COMPTON THRUST | 58.9( 94.8)| 6.8 | 0.078 | VII
ELYSIAN PARK THRUST | 61.8( 99.4)| 6.7 | 0.070 | VI
SAN JACINTO-SAN BERNARDINO | 61.9( 99.6 )| 6.7 | 0.049 | VI
*******************************************************************************
-END OF SEARCH- 18 FAULTS FOUND WITHIN THE SPECIFIED SEARCH RADIUS.
THE ROSE CANYON FAULT IS CLOSEST TO THE SITE.
IT IS ABOUT 5.3 MILES (8.6 km) AWAY.
LARGEST MAXIMUM-EARTHQUAKE SITE ACCELERATION: 0.5518 g
Page 2
W.O. 7103-A-SC
PLATE C-3
.001
.01
.1
1
1 10 100
STRIKE-SLIP FAULTS
11) Bozorgnia Campbell Niazi (1999) Hor.-Pleist. Soil-Cor. Acceleration (g)Distance [adist] (km)
M=5 M=6 M=7 M=8
W.O. 7103-A-SC
PLATE C-4
.001
.01
.1
1
.1 1 10
MAXIMUM EARTHQUAKES
SUMMERHILL Acceleration (g)Distance (mi)
W.O. 7103-A-SC
PLATE C-5
SITE
LEGEND
M = 4
M = 5
M = 6
M = 7
M = 8
-100
0
100
200
300
400
500
600
700
800
900
1000
1100
-400 -300 -200 -100 0 100 200 300 400 500 600
EARTHQUAKE EPICENTER MAP
SUMMERHILL
W.O. 7103-A-SC
PLATE C-6
7103-EQS
*************************
* *
* E Q S E A R C H *
* *
* Version 3.00 *
* *
*************************
ESTIMATION OF
PEAK ACCELERATION FROM
CALIFORNIA EARTHQUAKE CATALOGS
JOB NUMBER: 7103-A-SC
DATE: 06-29-2016
JOB NAME: SUMMERHILL
EARTHQUAKE-CATALOG-FILE NAME: C:\Program Files\EQSEARCH\ALLQUAKE.DAT
MAGNITUDE RANGE:
MINIMUM MAGNITUDE: 5.00
MAXIMUM MAGNITUDE: 9.00
SITE COORDINATES:
SITE LATITUDE: 33.1220
SITE LONGITUDE: 117.3020
SEARCH DATES:
START DATE: 1800
END DATE: 2016
SEARCH RADIUS:
62.4 mi
100.4 km
ATTENUATION RELATION: 12) Bozorgnia Campbell Niazi (1999) Hor.-Soft Rock-Cor.
UNCERTAINTY (M=Median, S=Sigma): S Number of Sigmas: 1.0
ASSUMED SOURCE TYPE: SS [SS=Strike-slip, DS=Reverse-slip, BT=Blind-thrust]
SCOND: 1 Depth Source: A
Basement Depth: .01 km Campbell SSR: 1 Campbell SHR: 0
COMPUTE PEAK HORIZONTAL ACCELERATION
MINIMUM DEPTH VALUE (km): 3.0
Page 1
W.O. 7103-A-SC
PLATE C-7
7103-EQS
-------------------------
EARTHQUAKE SEARCH RESULTS
-------------------------
Page 1
-------------------------------------------------------------------------------
| | | | TIME | | | SITE |SITE| APPROX.
FILE| LAT. | LONG. | DATE | (UTC) |DEPTH|QUAKE| ACC. | MM | DISTANCE
CODE| NORTH | WEST | | H M Sec| (km)| MAG.| g |INT.| mi [km]
----+-------+--------+----------+--------+-----+-----+-------+----+------------
DMG |33.0000|117.3000|11/22/1800|2130 0.0| 0.0| 6.50| 0.312 | IX | 8.4( 13.5)
MGI |33.0000|117.0000|09/21/1856| 730 0.0| 0.0| 5.00| 0.056 | VI | 19.4( 31.2)
MGI |32.8000|117.1000|05/25/1803| 0 0 0.0| 0.0| 5.00| 0.043 | VI | 25.1( 40.4)
DMG |32.7000|117.2000|05/27/1862|20 0 0.0| 0.0| 5.90| 0.062 | VI | 29.7( 47.8)
T-A |32.6700|117.1700|10/21/1862| 0 0 0.0| 0.0| 5.00| 0.033 | V | 32.1( 51.7)
T-A |32.6700|117.1700|12/00/1856| 0 0 0.0| 0.0| 5.00| 0.033 | V | 32.1( 51.7)
T-A |32.6700|117.1700|05/24/1865| 0 0 0.0| 0.0| 5.00| 0.033 | V | 32.1( 51.7)
PAS |32.9710|117.8700|07/13/1986|1347 8.2| 6.0| 5.30| 0.037 | V | 34.5( 55.5)
DMG |33.2000|116.7000|01/01/1920| 235 0.0| 0.0| 5.00| 0.030 | V | 35.2( 56.7)
DMG |32.8000|116.8000|10/23/1894|23 3 0.0| 0.0| 5.70| 0.044 | VI | 36.6( 58.9)
DMG |33.7000|117.4000|05/13/1910| 620 0.0| 0.0| 5.00| 0.026 | V | 40.3( 64.9)
DMG |33.7000|117.4000|05/15/1910|1547 0.0| 0.0| 6.00| 0.048 | VI | 40.3( 64.9)
DMG |33.7000|117.4000|04/11/1910| 757 0.0| 0.0| 5.00| 0.026 | V | 40.3( 64.9)
MGI |33.2000|116.6000|10/12/1920|1748 0.0| 0.0| 5.30| 0.031 | V | 40.9( 65.9)
DMG |33.6990|117.5110|05/31/1938| 83455.4| 10.0| 5.50| 0.034 | V | 41.6( 67.0)
DMG |33.7100|116.9250|09/23/1963|144152.6| 16.5| 5.00| 0.023 | IV | 46.0( 74.1)
DMG |33.7500|117.0000|06/06/1918|2232 0.0| 0.0| 5.00| 0.023 | IV | 46.7( 75.2)
DMG |33.7500|117.0000|04/21/1918|223225.0| 0.0| 6.80| 0.069 | VI | 46.7( 75.2)
MGI |33.8000|117.6000|04/22/1918|2115 0.0| 0.0| 5.00| 0.021 | IV | 49.9( 80.2)
DMG |33.8000|117.0000|12/25/1899|1225 0.0| 0.0| 6.40| 0.049 | VI | 49.9( 80.4)
DMG |33.5750|117.9830|03/11/1933| 518 4.0| 0.0| 5.20| 0.023 | IV | 50.2( 80.8)
DMG |33.0000|116.4330|06/04/1940|1035 8.3| 0.0| 5.10| 0.022 | IV | 51.0( 82.0)
DMG |33.6170|117.9670|03/11/1933| 154 7.8| 0.0| 6.30| 0.045 | VI | 51.4( 82.7)
PAS |33.5010|116.5130|02/25/1980|104738.5| 13.6| 5.50| 0.027 | V | 52.5( 84.5)
PDP |33.5080|116.5140|10/31/2001|075616.6| 15.0| 5.10| 0.021 | IV | 52.7( 84.8)
DMG |33.5000|116.5000|09/30/1916| 211 0.0| 0.0| 5.00| 0.020 | IV | 53.1( 85.5)
DMG |33.6170|118.0170|03/14/1933|19 150.0| 0.0| 5.10| 0.021 | IV | 53.5( 86.2)
DMG |33.9000|117.2000|12/19/1880| 0 0 0.0| 0.0| 6.00| 0.035 | V | 54.0( 87.0)
DMG |33.3430|116.3460|04/28/1969|232042.9| 20.0| 5.80| 0.029 | V | 57.3( 92.2)
DMG |33.6830|118.0500|03/11/1933| 658 3.0| 0.0| 5.50| 0.024 | V | 58.0( 93.3)
DMG |33.7000|118.0670|03/11/1933| 85457.0| 0.0| 5.10| 0.018 | IV | 59.5( 95.7)
DMG |33.7000|118.0670|03/11/1933| 51022.0| 0.0| 5.10| 0.018 | IV | 59.5( 95.7)
DMG |34.0000|117.2500|07/23/1923| 73026.0| 0.0| 6.25| 0.036 | V | 60.7( 97.7)
DMG |33.4000|116.3000|02/09/1890|12 6 0.0| 0.0| 6.30| 0.037 | V | 60.9( 98.1)
T-A |32.2500|117.5000|01/13/1877|20 0 0.0| 0.0| 5.00| 0.017 | IV | 61.3( 98.6)
MGI |34.0000|117.5000|12/16/1858|10 0 0.0| 0.0| 7.00| 0.059 | VI | 61.7( 99.3)
*******************************************************************************
-END OF SEARCH- 36 EARTHQUAKES FOUND WITHIN THE SPECIFIED SEARCH AREA.
TIME PERIOD OF SEARCH: 1800 TO 2016
LENGTH OF SEARCH TIME: 217 years
Page 2
W.O. 7103-A-SC
PLATE C-8
7103-EQS
THE EARTHQUAKE CLOSEST TO THE SITE IS ABOUT 8.4 MILES (13.5 km) AWAY.
LARGEST EARTHQUAKE MAGNITUDE FOUND IN THE SEARCH RADIUS: 7.0
LARGEST EARTHQUAKE SITE ACCELERATION FROM THIS SEARCH: 0.312 g
COEFFICIENTS FOR GUTENBERG & RICHTER RECURRENCE RELATION:
a-value= 0.608
b-value= 0.317
beta-value= 0.730
------------------------------------
TABLE OF MAGNITUDES AND EXCEEDANCES:
------------------------------------
Earthquake | Number of Times | Cumulative
Magnitude | Exceeded | No. / Year
-----------+-----------------+------------
4.0 | 36 | 0.16590
4.5 | 36 | 0.16590
5.0 | 36 | 0.16590
5.5 | 15 | 0.06912
6.0 | 9 | 0.04147
6.5 | 3 | 0.01382
7.0 | 1 | 0.00461
Page 3
W.O. 7103-A-SC
PLATE C-9
.001
.01
.1
1
1 10 100
STRIKE-SLIP FAULTS
12) Bozorgnia Campbell Niazi (1999) Hor.-Soft Rock-Cor. Acceleration (g)Distance [adist] (km)
M=5 M=6 M=7 M=8
W.O. 7103-A-SC
PLATE C-10
2
4
6
8
10
20
3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5 9.0
Number of Earthquakes (N) Above Magnitude (M)
SUMMERHILL Cumulative Number of Events (N)Magnitude (M)
W.O. 7103-A-SC
PLATE C-11
GeoSoils, Inc.
APPENDIX D
LABORATORY DATA
0
5
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
85
90
95
100
0.0010.010.1110100
2
B-1
60
LL PL
Depth D60D100
10 1001403
medium
1416
GRAIN SIZE DISTRIBUTION
GRAIN SIZE IN MILLIMETERS
COBBLES GRAVEL SAND
Sample
6
Sample
9.5
1.5
fine
D30
203/4 1/2
coarse
U.S. SIEVE NUMBERS
fine
3
0.18
404
2.5 52.5 40.8
30
B-1
200
Cu
%Gravel
HYDROMETERU.S. SIEVE OPENING IN INCHES
41
15.1
6 8
Sandy Clay, Qal
Visual Classification/USCS CLASSIFICATION
SILT OR CLAYPERCENT FINER BY WEIGHT15.1
coarse
PI Cc
D10 %Clay
RangeDepth
3/8
%Sand %Silt
50
GeoSoils, Inc.
5741 Palmer Way
Carlsbad, CA 92008
Telephone: (760) 438-3155
Fax: (760) 931-0915 Plate: D - 1
Project: SUMMERHILL
Number: 7103-A-SC
Date: July 2016US_GRAIN_SIZE 7103.GPJ US_LAB.GDT 7/6/16
-0.8
-0.6
-0.4
-0.2
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
100 1,000 10,000
H20
1000
Sample
Sandy Clay, Qal
MC
117.3STRAIN, %Initial
MCDepth/El.
Stress at which water was added: 500 psf
Strain Difference: _ _ _ _ _ _ %
Visual Classification
STRESS, psf
CONSOLIDATION TEST
B-1
Initial
13.1
Final
15.0 15.1
GeoSoils, Inc.
5741 Palmer Way
Carlsbad, CA 92008
Telephone: (760) 438-3155
Fax: (760) 931-0915 Plate: D - 2
Project: SUMMERHILL
Number: 7103-A-SC
Date: July 2016US_CONSOL_STRAIN 7103.GPJ US_LAB.GDT 7/6/16
Cal Land Engineering, Inc.
dba Quartech Consultant
Geotechnical, Environmental, and Civil Engineering
576 East Lambert Road, Brea, California 92821; Tel: 714-671-1050; Fax: 714-671-1090
SUMMARY OF LABORATORY TEST DATA
GeoSoils, Inc. QCI Project No.: 16-029-006n
5741 Palmer Way, Suite D Date: June 28, 2016
Carlsbad, CA 92010 Summarized by: KA
W.O. 7103-A-SC
Project Name: Summerhill
Client: N/A
Corrosivity Test Results
Sample ID
Sample
Depth
(ft)
pH
CT-532
(643)
Chloride
CT-422
(ppm)
Sulfate
CT-417
% By
Weight
Resistivity
CT-532 (643)
(ohm-cm)
B-1 3’-7’ 6.43 40 0.0375 350
B-2 5’ 5.53 35 0.0195 240
W.O. 7103-A-SC
PLATE D-3
GeoSoils, Inc.
APPENDIX E
LIQUEFACTION ANALYSIS
LiquefyPro CivilTech Software USA www.civiltech.comGeoSoils, Inc.
SEISMIC INDUCED LIQUEFACTION ANALYSIS
7103-A-SC Summerhill, FOS = 1.0
Tokimatsu/M-Correction; No Fines Correction, No Liquefiable Clays Plate E-1
Hole No.=B-2 Water Depth=16.5 ft Surface Elev.=100 Magnitude=7.2
Acceleration=0.464g
(ft)0
10
20
30
40
50
60
70
Remediated Fill: SANDY SILT, reddish
yellow to light brown, dry, medium dense,
broken rock/concrete encountered,
oxidation staining, fine grained sand
ALLUVIUM: Sandy Clay, dark reddish
brown, very moist, stiff, fine grained
SANTIAGO FORMATION: Claystone, light
yellow brown to yellowish gray, very moist
to wet becomes saturated at 21.5 feet, soft
Shear Stress Ratio
CRR CSR fs1
Shaded Zone has Liquefaction Potential
0 1
Soil DescriptionFactor of Safety
0 51
Settlement
Saturated
Unsaturat.
S = 0.14 in.
0 (in.) 1
fs1=1.00
LiquefyPro CivilTech Software USA www.civiltech.comGeoSoils, Inc.
SEISMIC INDUCED LIQUEFACTION ANALYSIS
7103-A-SC Summerhill, FOS = 1.3
Tokimatsu/M-Correction; No Fines Correction, No Liquefiable Clays Plate E-2
Hole No.=B-2 Water Depth=16.5 ft Surface Elev.=100 Magnitude=7.2
Acceleration=0.464g
(ft)0
10
20
30
40
50
60
70
Remediated Fill: SANDY SILT, reddish
yellow to light brown, dry, medium dense,
broken rock/concrete encountered,
oxidation staining, fine grained sand
ALLUVIUM: Sandy Clay, dark reddish
brown, very moist, stiff, fine grained
SANTIAGO FORMATION: Claystone, light
yellow brown to yellowish gray, very moist
to wet becomes saturated at 21.5 feet, soft
Shear Stress Ratio
CRR CSR fs1
Shaded Zone has Liquefaction Potential
0 1
Soil DescriptionFactor of Safety
0 51
Settlement
Saturated
Unsaturat.
S = 0.22 in.
0 (in.) 1
fs1=1.30
GeoSoils, Inc.
APPENDIX F
INFILTRATION DATA AND FORM I-8
GeoSoils, Inc.
Appendix I: Forms and Checklists
I-3 February 2016
Categorization of Infiltration Condition Form I-8
Part 1 - Full Infiltration Feasibility Screening Criteria
Would infiltration of the full design volume be feasible from a physical perspective without any undesirable consequences
that cannot be reasonably mitigated?
Criteria Screening Question Yes No
1
Is the estimated reliable infiltration rate below proposed facility locations greater
than 0.5 inches per hour? The response to this Screening Question shall be based on
a comprehensive evaluation of the factors presented in Appendix C.2 and Appendix D.
X
Provide basis:
GSI has evaluated the infiltration rate of natural surface soils on the west site to be about 0.2 inches/hour,
and on the east site to be about 0.5 inches/hour (both conducted in Hydrologic Soil Group A areas). Prior
development has resulted in the removal of natural surface soils, and for all intent and purposes, the west
site is predominantly a cut lot exposing some surfical fill and dense sedimentary bedrock consisting of silty
sandstone, and significant fill thickness exist on the east site. On the east site, artificial fill, created through
removal/recompaction of onsite soils is of a similar, very low permeability. See text of GSI (2016) for other
related discussions and references.
Summarize findings of studies; provide reference to studies, calculations, maps, data sources, etc. Provide narrative discussion
of study/data source applicability.
2
Can infiltration greater than 0.5 inches per hour be allowed without increasing
risk of geotechnical hazards (slope stability, groundwater mounding, utilities, or
other factors) that cannot be mitigated to an acceptable level? The response to this
Screening Question shall be based on a comprehensive evaluation of the factors
presented in Appendix C.2.
X
Provide basis:
See above. Groundwater was not encountered on the west site, and was encountered at a depth of about
21½ feet on the east site. There is an increased potential for the creation of perched groundwater
(mounding) conditions along zones of contrasting permeabilities, including shallow cut/fill contacts, fill lifts,
and transitions between clayey and sandy formational materials within the sedimentary bedrock. Due to
the strong permeability contrast between bedrock and fill, utility trenches can potentially act as french
drains and provide conduits for the movement of excessive moisture beneath the structure(s), exacerbating
slope instability, and fill and/or trench backfill settlement, causing distress to structures. See text of GSI
(2016) for other related discussions and references.
Summarize findings of studies; provide reference to studies, calculations, maps, data sources, etc. Provide narrative discussion
of study/data source applicability.
GeoSoils, Inc.
Appendix I: Forms and Checklists
I-4 February 2016
Form I-8 Page 2 of 4
Criteria Screening Question Yes No
3
Can infiltration greater than 0.5 inches per hour be allowed without increasing
risk of groundwater contamination (shallow water table, storm water pollutants
or other factors) that cannot be mitigated to an acceptable level? The response to
this Screening Question shall be based on a comprehensible evaluation of the factors
presented in Appendix C.3.
X
Provide basis:
While this study did not include an environmental assessment, visual observation did not indicate the
presence of potential contaminants. The infiltration rate is less than 0.5 inches per hour. While the regional
groundwater table is not considered a factor in the development of this site, the creation of a shallow
“perched” water table can occur through infiltration.
Summarize findings of studies; provide reference to studies, calculations, maps, data sources, etc. Provide narrative discussion
of study/data source applicability.
4
Can infiltration greater than 0.5 inches per hour be allowed without causing
potential water balance issues such as a change of seasonality of ephemeral streams
or increased discharge of contaminated groundwater to surface waters? The
response to this Screening Question shall be based on a comprehensive evaluation of
the factors presented in Appendix C.3.
X
Provide basis:
The infiltration rate is less than 0.5 inches per hour. The site currently appears to drain offsite and no runoff
appears to be retained onsite. While an environmental site assessment has not been performed to evaluate
the presence of contaminated groundwater, the regional groundwater table is not considered a factor in
the development of this site.
Summarize findings of studies; provide reference to studies, calculations, maps, data sources, etc. Provide narrative discussion
of study/data source applicability.
Part 1
Result*
In the answers to rows 1-4 are “Yes” a full infiltration design is potentially feasible. The feasibility
screening category is Full Infiltration
If any answer from row 1-4 is “No”, infiltration may be possible to some extent but would not generally
be feasible or desirable to achieve a “full infiltration” design.
Proceed to Part 2
* To be completed using gathered site information and best professional judgement considering the definition of MEP in the MS4
Permit. Additional testing and/or studies may be required by [City Engineer] to substantiate findings.
GeoSoils, Inc.
Appendix I: Forms and Checklists
I-5 February 2016
Form I-8 Page 3 of 4
Part 2 - Partial Infiltration vs. No Infiltration Feasibility Screening Criteria
Would infiltration of water in an appreciable amount be physically feasible without any negative consequences
that cannot be reasonably mitigated?
Criteria Screening Question Yes No
5
Do soil and geologic conditions allow for infiltration in any appreciable
rate or volume? The response to this Screening Question shall be based on
a comprehensive evaluation of the factors presented in Appendix C.2 and
Appendix D.
X
Provide basis:
GSI has evaluated the infiltration rate of natural surface soils on the west site to be about 0.2 inches/hour,
and on the east site to be about 0.5 inches/hour (both Hydrologic Soil Group A areas). Prior development
has resulted in the removal of natural surface soils, and for all intent and purposes, the west site is
predominantly a cut lot exposing some surfical fill and dense sedimentary bedrock consisting of silty
sandstone, and significant fill thickness exist on the east site. On the east site, artificial fill, created through
removal/recompaction of onsite soils is of a similar, very low permeability. See text of GSI (2016) for other
related discussions and references.
Summarize findings of studies; provide reference to studies, calculations, maps, data sources, etc. Provide narrative
discussion of study/data source applicability.
6
Can infiltration in any appreciable quantity be allowed without
increasing risk of geotechnical hazards (slope stability, groundwater
mounding, utilities, or other factors) that cannot be mitigated to an
acceptable level? The response to this Screening Question shall be based on
a comprehensive evaluation of the factors presented in Appendix C.2.
X
Provide basis:
No. The infiltration rate is less than 0.5 inches per hour. The limited permeability of sedimentary bedrock
will tend to result in the lateral migration of water and saturated conditions at, or near the surface,
increasing the potential for distress to foundations, floor slabs, and slope instability, etc. Onsite soils are
expansive, saturation of some onsite soils has been shown, through laboratory testing, to generate uplift
pressures on the order of 3,000 pounds per square. There is an increased potential for the creation of
perched groundwater (mounding) conditions along zones of contrasting permeabilities, including shallow
cut/fill contacts, fill lifts, and transitions between clayey and sandy formational materials within the
sedimentary bedrock. Due to the strong permeability contrast between bedrock and fill, utility trenches can
potentially act as french drains and provide conduits for the movement of excessive moisture beneath the
structure(s), exacerbating slope instability, and fill or backfill settlement, potentially causing distress to
structures. See text of GSI (2016) for other related discussions and references.
Summarize findings of studies; provide reference to studies, calculations, maps, data sources, etc. Provide narrative
discussion of study/data source applicability.
GeoSoils, Inc.
Appendix I: Forms and Checklists
I-6 February 2016
Form I-8 Page 4 of 4
Criteria Screening Question Yes No
7
Can Infiltration in any appreciable quantity be allowed without posing
significant risk for groundwater related concerns (shallow water table,
storm water pollutants or other factors)? The response to this Screening
Question shall be based on a comprehensive evaluation of the factors
presented in Appendix C.3.
X
Provide basis:
While the regional groundwater table is not considered a factor in the development of this site, the creation
of a shallow “perched” water table can occur and increase the potential for distress to the structure(s) due
to water vapor transmission through foundations, slabs, and any resultant corrosive effects on metal
conduit in trenches. See text of report for other related discussions and references.
Summarize findings of studies; provide reference to studies, calculations, maps, data sources, etc. Provide narrative
discussion of study/data source applicability.
8
Can infiltration be allowed without violating downstream water rights?
The response to this Screening Question shall be based on a comprehensive
evaluation of the factors presented in Appendix C.3.
X
Provide basis:
The infiltration rate is less than 0.5 inches per hour. The site currently appears to drain offsite and no runoff
appears to be retained onsite. While an environmental site assessment has not been performed to evaluate
the presence of contaminated groundwater, the regional groundwater table is not considered a factor in
the development of this site.
Summarize findings of studies; provide reference to studies, calculations, maps, data sources, etc. Provide narrative
discussion of study/data source applicability.
Part 2
Result*
If all answers from row 5-8 are yes then partial infiltration design is potentially feasible. The
feasibility screening category is Partial Infiltration.
If any answer from row 5-8 is no, then infiltration of any volume is considered to be
infeasible within the drainage area. The feasibility screening category is No Infiltration.
No
Infiltration
* To be completed using gathered site information and best professional judgement considering the definition of MEP in the MS4
Permit. Additional testing and/or studies may be required by Agency/Jurisdictions to substantiate findings.
GeoSoils, Inc.
APPENDIX G
GENERAL EARTHWORK, GRADING GUIDELINES
AND PRELIMINARY CRITERIA
GeoSoils, Inc.
GENERAL EARTHWORK, GRADING GUIDELINES, AND PRELIMINARY CRITERIA
General
These guidelines present general procedures and requirements for earthwork and grading
as shown on the approved grading plans, including preparation of areas to be filled,
placement of fill, installation of subdrains, excavations, and appurtenant structures or
flatwork. The recommendations contained in the geotechnical report are part of these
earthwork and grading guidelines and would supercede the provisions contained hereafter
in the case of conflict. Evaluations performed by the consultant during the course of
grading may result in new or revised recommendations which could supercede these
guidelines or the recommendations contained in the geotechnical report. Generalized
details follow this text.
The contractor is responsible for the satisfactory completion of all earthwork in accordance
with provisions of the project plans and specifications and latest adopted code. In the case
of conflict, the most onerous provisions shall prevail. The project geotechnical engineer
and engineering geologist (geotechnical consultant), and/or their representatives, should
provide observation and testing services, and geotechnical consultation during the
duration of the project.
EARTHWORK OBSERVATIONS AND TESTING
Geotechnical Consultant
Prior to the commencement of grading, a qualified geotechnical consultant (soil engineer
and engineering geologist) should be employed for the purpose of observing earthwork
procedures and testing the fills for general conformance with the recommendations of the
geotechnical report(s), the approved grading plans, and applicable grading codes and
ordinances.
The geotechnical consultant should provide testing and observation so that an evaluation
may be made that the work is being accomplished as specified. It is the responsibility of
the contractor to assist the consultants and keep them apprised of anticipated work
schedules and changes, so that they may schedule their personnel accordingly.
All remedial removals, clean-outs, prepared ground to receive fill, key excavations, and
subdrain installation should be observed and documented by the geotechnical consultant
prior to placing any fill. It is the contractor’s responsibility to notify the geotechnical
consultant when such areas are ready for observation.
Laboratory and Field Tests
Maximum dry density tests to determine the degree of compaction should be performed
in accordance with American Standard Testing Materials test method ASTM designation
D-1557. Random or representative field compaction tests should be performed in
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File:e:\wp12\7103\7103a.pge Page 2
accordance with test methods ASTM designation D-1556, D-2937 or D-2922, and D-3017,
at intervals of approximately ±2 feet of fill height or approximately every 1,000 cubic yards
placed. These criteria would vary depending on the soil conditions and the size of the
project. The location and frequency of testing would be at the discretion of the
geotechnical consultant.
Contractor's Responsibility
All clearing, site preparation, and earthwork performed on the project should be conducted
by the contractor, with observation by a geotechnical consultant, and staged approval by
the governing agencies, as applicable. It is the contractor's responsibility to prepare the
ground surface to receive the fill, to the satisfaction of the geotechnical consultant, and to
place, spread, moisture condition, mix, and compact the fill in accordance with the
recommendations of the geotechnical consultant. The contractor should also remove all
non-earth material considered unsatisfactory by the geotechnical consultant.
Notwithstanding the services provided by the geotechnical consultant, it is the sole
responsibility of the contractor to provide adequate equipment and methods to accomplish
the earthwork in strict accordance with applicable grading guidelines, latest adopted codes
or agency ordinances, geotechnical report(s), and approved grading plans. Sufficient
watering apparatus and compaction equipment should be provided by the contractor with
due consideration for the fill material, rate of placement, and climatic conditions. If, in the
opinion of the geotechnical consultant, unsatisfactory conditions such as questionable
weather, excessive oversized rock or deleterious material, insufficient support equipment,
etc., are resulting in a quality of work that is not acceptable, the consultant will inform the
contractor, and the contractor is expected to rectify the conditions, and if necessary, stop
work until conditions are satisfactory.
During construction, the contractor shall properly grade all surfaces to maintain good
drainage and prevent ponding of water. The contractor shall take remedial measures to
control surface water and to prevent erosion of graded areas until such time as permanent
drainage and erosion control measures have been installed.
SITE PREPARATION
All major vegetation, including brush, trees, thick grasses, organic debris, and other
deleterious material, should be removed and disposed of off-site. These removals must
be concluded prior to placing fill. In-place existing fill, soil, alluvium, colluvium, or rock
materials, as evaluated by the geotechnical consultant as being unsuitable, should be
removed prior to any fill placement. Depending upon the soil conditions, these materials
may be reused as compacted fills. Any materials incorporated as part of the compacted
fills should be approved by the geotechnical consultant.
Any underground structures such as cesspools, cisterns, mining shafts, tunnels, septic
tanks, wells, pipelines, or other structures not located prior to grading, are to be removed
GeoSoils, Inc.Summerhill Homes Appendix G
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or treated in a manner recommended by the geotechnical consultant. Soft, dry, spongy,
highly fractured, or otherwise unsuitable ground, extending to such a depth that surface
processing cannot adequately improve the condition, should be overexcavated down to
firm ground and approved by the geotechnical consultant before compaction and filling
operations continue. Overexcavated and processed soils, which have been properly
mixed and moisture conditioned, should be re-compacted to the minimum relative
compaction as specified in these guidelines.
Existing ground, which is determined to be satisfactory for support of the fills, should be
scarified (ripped) to a minimum depth of 6 to 8 inches, or as directed by the geotechnical
consultant. After the scarified ground is brought to optimum moisture content, or greater
and mixed, the materials should be compacted as specified herein. If the scarified zone
is greater than 6 to 8 inches in depth, it may be necessary to remove the excess and place
the material in lifts restricted to about 6 to 8 inches in compacted thickness.
Existing ground which is not satisfactory to support compacted fill should be
overexcavated as required in the geotechnical report, or by the on-site geotechnical
consultant. Scarification, disc harrowing, or other acceptable forms of mixing should
continue until the soils are broken down and free of large lumps or clods, until the working
surface is reasonably uniform and free from ruts, hollows, hummocks, mounds, or other
uneven features, which would inhibit compaction as described previously.
Where fills are to be placed on ground with slopes steeper than 5:1 (horizontal to vertical
[h:v]), the ground should be stepped or benched. The lowest bench, which will act as a
key, should be a minimum of 15 feet wide and should be at least 2 feet deep into firm
material, and approved by the geotechnical consultant. In fill-over-cut slope conditions,
the recommended minimum width of the lowest bench or key is also 15 feet, with the key
founded on firm material, as designated by the geotechnical consultant. As a general rule,
unless specifically recommended otherwise by the geotechnical consultant, the minimum
width of fill keys should be equal to ½ the height of the slope.
Standard benching is generally 4 feet (minimum) vertically, exposing firm, acceptable
material. Benching may be used to remove unsuitable materials, although it is understood
that the vertical height of the bench may exceed 4 feet. Pre-stripping may be considered
for unsuitable materials in excess of 4 feet in thickness.
All areas to receive fill, including processed areas, removal areas, and the toes of fill
benches, should be observed and approved by the geotechnical consultant prior to
placement of fill. Fills may then be properly placed and compacted until design grades
(elevations) are attained.
COMPACTED FILLS
Any earth materials imported or excavated on the property may be utilized in the fill
provided that each material has been evaluated to be suitable by the geotechnical
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consultant. These materials should be free of roots, tree branches, other organic matter,
or other deleterious materials. All unsuitable materials should be removed from the fill as
directed by the geotechnical consultant. Soils of poor gradation, undesirable expansion
potential, or substandard strength characteristics may be designated by the consultant as
unsuitable and may require blending with other soils to serve as a satisfactory fill material.
Fill materials derived from benching operations should be dispersed throughout the fill
area and blended with other approved material. Benching operations should not result in
the benched material being placed only within a single equipment width away from the
fill/bedrock contact.
Oversized materials defined as rock, or other irreducible materials, with a maximum
dimension greater than 12 inches, should not be buried or placed in fills unless the
location of materials and disposal methods are specifically approved by the geotechnical
consultant. Oversized material should be taken offsite, or placed in accordance with
recommendations of the geotechnical consultant in areas designated as suitable for rock
disposal. GSI anticipates that soils to be utilized as fill material for the subject project may
contain some rock. Appropriately, the need for rock disposal may be necessary during
grading operations on the site. From a geotechnical standpoint, the depth of any rocks,
rock fills, or rock blankets, should be a sufficient distance from finish grade. This depth is
generally the same as any overexcavation due to cut-fill transitions in hard rock areas, and
generally facilitates the excavation of structural footings and substructures. Should deeper
excavations be proposed (i.e., deepened footings, utility trenching, swimming pools, spas,
etc.), the developer may consider increasing the hold-down depth of any rocky fills to be
placed, as appropriate. In addition, some agencies/jurisdictions mandate a specific
hold-down depth for oversize materials placed in fills. The hold-down depth, and potential
to encounter oversize rock, both within fills, and occurring in cut or natural areas, would
need to be disclosed to all interested/affected parties. Once approved by the governing
agency, the hold-down depth for oversized rock (i.e., greater than 12 inches) in fills on this
project is provided as 10 feet, unless specified differently in the text of this report. The
governing agency may require that these materials need to be deeper, crushed, or
reduced to less than 12 inches in maximum dimension, at their discretion.
To facilitate future trenching, rock (or oversized material), should not be placed within the
hold-down depth feet from finish grade, the range of foundation excavations, future utilities,
or underground construction unless specifically approved by the governing agency, the
geotechnical consultant, and/or the developer’s representative.
If import material is required for grading, representative samples of the materials to be
utilized as compacted fill should be analyzed in the laboratory by the geotechnical
consultant to evaluate it’s physical properties and suitability for use onsite. Such testing
should be performed three (3) days prior to importation. If any material other than that
previously tested is encountered during grading, an appropriate analysis of this material
should be conducted by the geotechnical consultant as soon as possible.
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Approved fill material should be placed in areas prepared to receive fill in near horizontal
layers, that when compacted, should not exceed about 6 to 8 inches in thickness. The
geotechnical consultant may approve thick lifts if testing indicates the grading procedures
are such that adequate compaction is being achieved with lifts of greater thickness. Each
layer should be spread evenly and blended to attain uniformity of material and moisture
suitable for compaction.
Fill layers at a moisture content less than optimum should be watered and mixed, and wet
fill layers should be aerated by scarification, or should be blended with drier material.
Moisture conditioning, blending, and mixing of the fill layer should continue until the fill
materials have a uniform moisture content at, or above, optimum moisture.
After each layer has been evenly spread, moisture conditioned, and mixed, it should be
uniformly compacted to a minimum of 90 percent of the maximum density as evaluated by
ASTM test designation D 1557, or as otherwise recommended by the geotechnical
consultant. Compaction equipment should be adequately sized and should be specifically
designed for soil compaction, or of proven reliability to efficiently achieve the specified
degree of compaction.
Where tests indicate that the density of any layer of fill, or portion thereof, is below the
required relative compaction, or improper moisture is in evidence, the particular layer or
portion shall be re-worked until the required density and/or moisture content has been
attained. No additional fill shall be placed in an area until the last placed lift of fill has been
tested and found to meet the density and moisture requirements, and is approved by the
geotechnical consultant.
In general, per the latest adopted version of the California Building Code (CBC), fill slopes
should be designed and constructed at a gradient of 2:1 (h:v), or flatter. Compaction of
slopes should be accomplished by over-building a minimum of 3 feet horizontally, and
subsequently trimming back to the design slope configuration. Testing shall be performed
as the fill is elevated to evaluate compaction as the fill core is being developed. Special
efforts may be necessary to attain the specified compaction in the fill slope zone. Final
slope shaping should be performed by trimming and removing loose materials with
appropriate equipment. A final evaluation of fill slope compaction should be based on
observation and/or testing of the finished slope face. Where compacted fill slopes are
designed steeper than 2:1 (h:v), prior approval from the governing agency, specific
material types, a higher minimum relative compaction, special reinforcement, and special
grading procedures will be recommended.
If an alternative to over-building and cutting back the compacted fill slopes is selected,
then special effort should be made to achieve the required compaction in the outer 10 feet
of each lift of fill by undertaking the following:
1.An extra piece of equipment consisting of a heavy, short-shanked sheepsfoot
should be used to roll (horizontal) parallel to the slopes continuously as fill is
placed. The sheepsfoot roller should also be used to roll perpendicular to the
GeoSoils, Inc.Summerhill Homes Appendix G
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slopes, and extend out over the slope to provide adequate compaction to the face
of the slope.
2.Loose fill should not be spilled out over the face of the slope as each lift is
compacted. Any loose fill spilled over a previously completed slope face should be
trimmed off or be subject to re-rolling.
3.Field compaction tests will be made in the outer (horizontal) ±2 to ±8 feet of the
slope at appropriate vertical intervals, subsequent to compaction operations.
4.After completion of the slope, the slope face should be shaped with a small tractor
and then re-rolled with a sheepsfoot to achieve compaction to near the slope face.
Subsequent to testing to evaluate compaction, the slopes should be grid-rolled to
achieve compaction to the slope face. Final testing should be used to evaluate
compaction after grid rolling.
5.Where testing indicates less than adequate compaction, the contractor will be
responsible to rip, water, mix, and recompact the slope material as necessary to
achieve compaction. Additional testing should be performed to evaluate
compaction.
SUBDRAIN INSTALLATION
Subdrains should be installed in approved ground in accordance with the approximate
alignment and details indicated by the geotechnical consultant. Subdrain locations or
materials should not be changed or modified without approval of the geotechnical
consultant. The geotechnical consultant may recommend and direct changes in subdrain
line, grade, and drain material in the field, pending exposed conditions. The location of
constructed subdrains, especially the outlets, should be recorded/surveyed by the project
civil engineer. Drainage at the subdrain outlets should be provided by the project civil
engineer.
EXCAVATIONS
Excavations and cut slopes should be examined during grading by the geotechnical
consultant. If directed by the geotechnical consultant, further excavations or
overexcavation and refilling of cut areas should be performed, and/or remedial grading of
cut slopes should be performed. When fill-over-cut slopes are to be graded, unless
otherwise approved, the cut portion of the slope should be observed by the geotechnical
consultant prior to placement of materials for construction of the fill portion of the slope.
The geotechnical consultant should observe all cut slopes, and should be notified by the
contractor when excavation of cut slopes commence.
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If, during the course of grading, unforeseen adverse or potentially adverse geologic
conditions are encountered, the geotechnical consultant should investigate, evaluate, and
make appropriate recommendations for mitigation of these conditions. The need for cut
slope buttressing or stabilizing should be based on in-grading evaluation by the
geotechnical consultant, whether anticipated or not.
Unless otherwise specified in geotechnical and geological report(s), no cut slopes should
be excavated higher or steeper than that allowed by the ordinances of controlling
governmental agencies. Additionally, short-term stability of temporary cut slopes is the
contractor’s responsibility.
Erosion control and drainage devices should be designed by the project civil engineer and
should be constructed in compliance with the ordinances of the controlling governmental
agencies, and/or in accordance with the recommendations of the geotechnical consultant.
COMPLETION
Observation, testing, and consultation by the geotechnical consultant should be
conducted during the grading operations in order to state an opinion that all cut and fill
areas are graded in accordance with the approved project specifications. After completion
of grading, and after the geotechnical consultant has finished observations of the work,
final reports should be submitted, and may be subject to review by the controlling
governmental agencies. No further excavation or filling should be undertaken without prior
notification of the geotechnical consultant or approved plans.
All finished cut and fill slopes should be protected from erosion and/or be planted in
accordance with the project specifications and/or as recommended by a landscape
architect. Such protection and/or planning should be undertaken as soon as practical after
completion of grading.
PRELIMINARY OUTDOOR POOL/SPA DESIGN RECOMMENDATIONS
The following preliminary recommendations are provided for consideration in pool/spa
design and planning. Actual recommendations should be provided by a qualified
geotechnical consultant, based on site specific geotechnical conditions, including a
subsurface investigation, differential settlement potential, expansive and corrosive soil
potential, proximity of the proposed pool/spa to any slopes with regard to slope creep and
lateral fill extension, as well as slope setbacks per Code, and geometry of the proposed
improvements. Recommendations for pools/spas and/or deck flatwork underlain by
expansive soils, or for areas with differential settlement greater than ¼-inch over 40 feet
horizontally, will be more onerous than the preliminary recommendations presented below.
The 1:1 (h:v) influence zone of any nearby retaining wall site structures should be
delineated on the project civil drawings with the pool/spa. This 1:1 (h:v) zone is defined
as a plane up from the lower-most heel of the retaining structure, to the daylight grade of
GeoSoils, Inc.Summerhill Homes Appendix G
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the nearby building pad or slope. If pools/spas or associated pool/spa improvements are
constructed within this zone, they should be re-positioned (horizontally or vertically) so that
they are supported by earth materials that are outside or below this 1:1 plane. If this is not
possible given the area of the building pad, the owner should consider eliminating these
improvements or allow for increased potential for lateral/vertical deformations and
associated distress that may render these improvements unusable in the future, unless
they are periodically repaired and maintained. The conditions and recommendations
presented herein should be disclosed to all homeowners and any interested/affected
parties.
General
1.The equivalent fluid pressure to be used for the pool/spa design should be
60 pounds per cubic foot (pcf) for pool/spa walls with level backfill, and 75 pcf for
a 2:1 sloped backfill condition. In addition, backdrains should be provided behind
pool/spa walls subjacent to slopes.
2.Passive earth pressure may be computed as an equivalent fluid having a density of
150 pcf, to a maximum lateral earth pressure of 1,000 pounds per square foot (psf).
3.An allowable coefficient of friction between soil and concrete of 0.30 may be used
with the dead load forces.
4.When combining passive pressure and frictional resistance, the passive pressure
component should be reduced by one-third.
5.Where pools/spas are planned near structures, appropriate surcharge loads need
to be incorporated into design and construction by the pool/spa designer. This
includes, but is not limited to landscape berms, decorative walls, footings, built-in
barbeques, utility poles, etc.
6.All pool/spa walls should be designed as “free standing” and be capable of
supporting the water in the pool/spa without soil support. The shape of pool/spa
in cross section and plan view may affect the performance of the pool, from a
geotechnical standpoint. Pools and spas should also be designed in accordance
with the latest adopted Code. Minimally, the bottoms of the pools/spas, should
maintain a distance H/3, where H is the height of the slope (in feet), from the slope
face. This distance should not be less than 7 feet, nor need not be greater than
40 feet.
7.The soil beneath the pool/spa bottom should be uniformly moist with the same
stiffness throughout. If a fill/cut transition occurs beneath the pool/spa bottom, the
cut portion should be overexcavated to a minimum depth of 48 inches, and
replaced with compacted fill, such that there is a uniform blanket that is a minimum
of 48 inches below the pool/spa shell. If very low expansive soil is used for fill, the
fill should be placed at a minimum of 95 percent relative compaction, at optimum
GeoSoils, Inc.Summerhill Homes Appendix G
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moisture conditions. This requirement should be 90 percent relative compaction
at over optimum moisture if the pool/spa is constructed within or near expansive
soils. The potential for grading and/or re-grading of the pool/spa bottom, and
attendant potential for shoring and/or slot excavation, needs to be considered
during all aspects of pool/spa planning, design, and construction.
8.If the pool/spa is founded entirely in compacted fill placed during rough grading, the
deepest portion of the pool/spa should correspond with the thickest fill on the lot.
9.Hydrostatic pressure relief valves should be incorporated into the pool and spa
designs. A pool/spa under-drain system is also recommended, with an appropriate
outlet for discharge.
10.All fittings and pipe joints, particularly fittings in the side of the pool or spa, should
be properly sealed to prevent water from leaking into the adjacent soils materials,
and be fitted with slip or expandible joints between connections transecting varying
soil conditions.
11.An elastic expansion joint (flexible waterproof sealant) should be installed to prevent
water from seeping into the soil at all deck joints.
12.A reinforced grade beam should be placed around skimmer inlets to provide
support and mitigate cracking around the skimmer face.
13.In order to reduce unsightly cracking, deck slabs should minimally be 4 inches
thick, and reinforced with No. 3 reinforcing bars at 18 inches on-center. All slab
reinforcement should be supported to ensure proper mid-slab positioning during
the placement of concrete. Wire mesh reinforcing is specifically not recommended.
Deck slabs should not be tied to the pool/spa structure. Pre-moistening and/or
pre-soaking of the slab subgrade is recommended, to a depth of 12 inches
(optimum moisture content), or 18 inches (120 percent of the soil’s optimum
moisture content, or 3 percent over optimum moisture content, whichever is
greater), for very low to low, and medium expansive soils, respectively. This
moisture content should be maintained in the subgrade soils during concrete
placement to promote uniform curing of the concrete and minimize the
development of unsightly shrinkage cracks. Slab underlayment should consist of
a 1- to 2-inch leveling course of sand (S.E.>30) and a minimum of 4 to 6 inches of
Class 2 base compacted to 90 percent. Deck slabs within the H/3 zone, where H
is the height of the slope (in feet), will have an increased potential for distress
relative to other areas outside of the H/3 zone. If distress is undesirable,
improvements, deck slabs or flatwork should not be constructed closer than H/3 or
7 feet (whichever is greater) from the slope face, in order to reduce, but not
eliminate, this potential.
14.Pool/spa bottom or deck slabs should be founded entirely on competent bedrock,
or properly compacted fill. Fill should be compacted to achieve a minimum
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90 percent relative compaction, as discussed above. Prior to pouring concrete,
subgrade soils below the pool/spa decking should be throughly watered to achieve
a moisture content that is at least 2 percent above optimum moisture content, to a
depth of at least 18 inches below the bottom of slabs. This moisture content should
be maintained in the subgrade soils during concrete placement to promote uniform
curing of the concrete and minimize the development of unsightly shrinkage cracks.
15.In order to reduce unsightly cracking, the outer edges of pool/spa decking to be
bordered by landscaping, and the edges immediately adjacent to the pool/spa,
should be underlain by an 8-inch wide concrete cutoff shoulder (thickened edge)
extending to a depth of at least 12 inches below the bottoms of the slabs to mitigate
excessive infiltration of water under the pool/spa deck. These thickened edges
should be reinforced with two No. 4 bars, one at the top and one at the bottom.
Deck slabs may be minimally reinforced with No. 3 reinforcing bars placed at
18 inches on-center, in both directions. All slab reinforcement should be supported
on chairs to ensure proper mid-slab positioning during the placement of concrete.
16.Surface and shrinkage cracking of the finish slab may be reduced if a low slump
and water-cement ratio are maintained during concrete placement. Concrete
utilized should have a minimum compressive strength of 4,000 psi. Excessive water
added to concrete prior to placement is likely to cause shrinkage cracking, and
should be avoided. Some concrete shrinkage cracking, however, is unavoidable.
17.Joint and sawcut locations for the pool/spa deck should be determined by the
design engineer and/or contractor. However, spacings should not exceed 6 feet on
center.
18.Considering the nature of the onsite earth materials, it should be anticipated that
caving or sloughing could be a factor in subsurface excavations and trenching.
Shoring or excavating the trench walls/backcuts at the angle of repose (typically 25
to 45 degrees), should be anticipated. All excavations should be observed by a
representative of the geotechnical consultant, including the project geologist and/or
geotechnical engineer, prior to workers entering the excavation or trench, and
minimally conform to Cal/OSHA (“Type C” soils may be assumed), state, and local
safety codes. Should adverse conditions exist, appropriate recommendations
should be offered at that time by the geotechnical consultant. GSI does not consult
in the area of safety engineering and the safety of the construction crew is the
responsibility of the pool/spa builder.
19.It is imperative that adequate provisions for surface drainage are incorporated by
the homeowners into their overall improvement scheme. Ponding water, ground
saturation and flow over slope faces, are all situations which must be avoided to
enhance long-term performance of the pool/spa and associated improvements, and
reduce the likelihood of distress.
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20.Regardless of the methods employed, once the pool/spa is filled with water, should
it be emptied, there exists some potential that if emptied, significant distress may
occur. Accordingly, once filled, the pool/spa should not be emptied unless
evaluated by the geotechnical consultant and the pool/spa builder.
21.For pools/spas built within (all or part) of the Code setback and/or geotechnical
setback, as indicated in the site geotechnical documents, special foundations are
recommended to mitigate the affects of creep, lateral fill extension, expansive soils
and settlement on the proposed pool/spa. Most municipalities or County reviewers
do not consider these effects in pool/spa plan approvals. As such, where
pools/spas are proposed on 20 feet or more of fill, medium or highly expansive
soils, or rock fill with limited “cap soils” and built within Code setbacks, or within the
influence of the creep zone, or lateral fill extension, the following should be
considered during design and construction:
OPTION A: Shallow foundations with or without overexcavation of the
pool/spa “shell,” such that the pool/spa is surrounded by 5 feet of very low
to low expansive soils (without irreducible particles greater that 6 inches),
and the pool/spa walls closer to the slope(s) are designed to be free
standing. GSI recommends a pool/spa under-drain or blanket system (see
attached Typical Pool/Spa Detail). The pool/spa builders and owner in this
optional construction technique should be generally satisfied with pool/spa
performance under this scenario; however, some settlement, tilting, cracking,
and leakage of the pool/spa is likely over the life of the project.
OPTION B: Pier supported pool/spa foundations with or without
overexcavation of the pool/spa shell such that the pool/spa is surrounded by
5 feet of very low to low expansive soils (without irreducible particles greater
than 6 inches), and the pool/spa walls closer to the slope(s) are designed to
be free standing. The need for a pool/spa under-drain system may be
installed for leak detection purposes. Piers that support the pool/spa should
be a minimum of 12 inches in diameter and at a spacing to provide vertical
and lateral support of the pool/spa, in accordance with the pool/spa
designers recommendations current applicable Codes. The pool/spa builder
and owner in this second scenario construction technique should be more
satisfied with pool/spa performance. This construction will reduce settlement
and creep effects on the pool/spa; however, it will not eliminate these
potentials, nor make the pool/spa “leak-free.”
22.The temperature of the water lines for spas and pools may affect the corrosion
properties of site soils, thus, a corrosion specialist should be retained to review all
spa and pool plans, and provide mitigative recommendations, as warranted.
Concrete mix design should be reviewed by a qualified corrosion consultant and
materials engineer.
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23.All pool/spa utility trenches should be compacted to 90 percent of the laboratory
standard, under the full-time observation and testing of a qualified geotechnical
consultant. Utility trench bottoms should be sloped away from the primary structure
on the property (typically the residence).
24.Pool and spa utility lines should not cross the primary structure’s utility lines (i.e.,
not stacked, or sharing of trenches, etc.).
25.The pool/spa or associated utilities should not intercept, interrupt, or otherwise
adversely impact any area drain, roof drain, or other drainage conveyances. If it is
necessary to modify, move, or disrupt existing area drains, subdrains, or tightlines,
then the design civil engineer should be consulted, and mitigative measures
provided. Such measures should be further reviewed and approved by the
geotechnical consultant, prior to proceeding with any further construction.
26.The geotechnical consultant should review and approve all aspects of pool/spa and
flatwork design prior to construction. A design civil engineer should review all
aspects of such design, including drainage and setback conditions. Prior to
acceptance of the pool/spa construction, the project builder, geotechnical
consultant and civil designer should evaluate the performance of the area drains
and other site drainage pipes, following pool/spa construction.
27.All aspects of construction should be reviewed and approved by the geotechnical
consultant, including during excavation, prior to the placement of any additional fill,
prior to the placement of any reinforcement or pouring of any concrete.
28.Any changes in design or location of the pool/spa should be reviewed and
approved by the geotechnical and design civil engineer prior to construction. Field
adjustments should not be allowed until written approval of the proposed field
changes are obtained from the geotechnical and design civil engineer.
29.Disclosure should be made to homeowners and builders, contractors, and any
interested/affected parties, that pools/spas built within about 15 feet of the top of a
slope, and/or H/3, where H is the height of the slope (in feet), will experience some
movement or tilting. While the pool/spa shell or coping may not necessarily crack,
the levelness of the pool/spa will likely tilt toward the slope, and may not be
esthetically pleasing. The same is true with decking, flatwork and other
improvements in this zone.
30.Failure to adhere to the above recommendations will significantly increase the
potential for distress to the pool/spa, flatwork, etc.
31.Local seismicity and/or the design earthquake will cause some distress to the
pool/spa and decking or flatwork, possibly including total functional and economic
loss.
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32.The information and recommendations discussed above should be provided to any
contractors and/or subcontractors, or homeowners, interested/affected parties, etc.,
that may perform or may be affected by such work.
JOB SAFETY
General
At GSI, getting the job done safely is of primary concern. The following is the company's
safety considerations for use by all employees on multi-employer construction sites.
On-ground personnel are at highest risk of injury, and possible fatality, on grading and
construction projects. GSI recognizes that construction activities will vary on each site, and
that site safety is the prime responsibility of the contractor; however, everyone must be
safety conscious and responsible at all times. To achieve our goal of avoiding accidents,
cooperation between the client, the contractor, and GSI personnel must be maintained.
In an effort to minimize risks associated with geotechnical testing and observation, the
following precautions are to be implemented for the safety of field personnel on grading
and construction projects:
Safety Meetings: GSI field personnel are directed to attend contractor’s regularly
scheduled and documented safety meetings.
Safety Vests: Safety vests are provided for, and are to be worn by GSI personnel,
at all times, when they are working in the field.
Safety Flags:Two safety flags are provided to GSI field technicians; one is to be
affixed to the vehicle when on site, the other is to be placed atop the
spoil pile on all test pits.
Flashing Lights:All vehicles stationary in the grading area shall use rotating or flashing
amber beacons, or strobe lights, on the vehicle during all field testing.
While operating a vehicle in the grading area, the emergency flasher
on the vehicle shall be activated.
In the event that the contractor's representative observes any of our personnel not
following the above, we request that it be brought to the attention of our office.
Test Pits Location, Orientation, and Clearance
The technician is responsible for selecting test pit locations. A primary concern should be
the technician’s safety. Efforts will be made to coordinate locations with the grading
contractor’s authorized representative, and to select locations following or behind the
established traffic pattern, preferably outside of current traffic. The contractor’s authorized
representative (supervisor, grade checker, dump man, operator, etc.) should direct
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excavation of the pit and safety during the test period. Of paramount concern should be
the soil technician’s safety, and obtaining enough tests to represent the fill.
Test pits should be excavated so that the spoil pile is placed away from oncoming traffic,
whenever possible. The technician's vehicle is to be placed next to the test pit, opposite
the spoil pile. This necessitates the fill be maintained in a driveable condition.
Alternatively, the contractor may wish to park a piece of equipment in front of the test
holes, particularly in small fill areas or those with limited access.
A zone of non-encroachment should be established for all test pits. No grading equipment
should enter this zone during the testing procedure. The zone should extend
approximately 50 feet outward from the center of the test pit. This zone is established for
safety and to avoid excessive ground vibration, which typically decreases test results.
When taking slope tests, the technician should park the vehicle directly above or below the
test location. If this is not possible, a prominent flag should be placed at the top of the
slope. The contractor's representative should effectively keep all equipment at a safe
operational distance (e.g., 50 feet) away from the slope during this testing.
The technician is directed to withdraw from the active portion of the fill as soon as possible
following testing. The technician's vehicle should be parked at the perimeter of the fill in
a highly visible location, well away from the equipment traffic pattern. The contractor
should inform our personnel of all changes to haul roads, cut and fill areas or other factors
that may affect site access and site safety.
In the event that the technician’s safety is jeopardized or compromised as a result of the
contractor’s failure to comply with any of the above, the technician is required, by company
policy, to immediately withdraw and notify his/her supervisor. The grading contractor’s
representative will be contacted in an effort to affect a solution. However, in the interim,
no further testing will be performed until the situation is rectified. Any fill placed can be
considered unacceptable and subject to reprocessing, recompaction, or removal.
In the event that the soil technician does not comply with the above or other established
safety guidelines, we request that the contractor bring this to the technician’s attention and
notify this office. Effective communication and coordination between the contractor’s
representative and the soil technician is strongly encouraged in order to implement the
above safety plan.
Trench and Vertical Excavation
It is the contractor's responsibility to provide safe access into trenches where compaction
testing is needed. Our personnel are directed not to enter any excavation or vertical cut
which: 1) is 5 feet or deeper unless shored or laid back; 2) displays any evidence of
instability, has any loose rock or other debris which could fall into the trench; or 3) displays
any other evidence of any unsafe conditions regardless of depth.
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All trench excavations or vertical cuts in excess of 5 feet deep, which any person enters,
should be shored or laid back. Trench access should be provided in accordance with
Cal/OSHA and/or state and local standards. Our personnel are directed not to enter any
trench by being lowered or “riding down” on the equipment.
If the contractor fails to provide safe access to trenches for compaction testing, our
company policy requires that the soil technician withdraw and notify his/her supervisor.
The contractor’s representative will be contacted in an effort to affect a solution. All backfill
not tested due to safety concerns or other reasons could be subject to reprocessing and/or
removal.
If GSI personnel become aware of anyone working beneath an unsafe trench wall or
vertical excavation, we have a legal obligation to put the contractor and owner/developer
on notice to immediately correct the situation. If corrective steps are not taken, GSI then
has an obligation to notify Cal/OSHA and/or the proper controlling authorities.
Appendix E.2
Supplemental Geotechnical
Recommendations
Geotechnical C Geologic C Coastal C Environmental
5741 Palmer Way C Carlsbad, California 92010 C (760) 438-3155 C FAX (760) 931-0915 C www.geosoilsinc.com
July 11, 2018
W.O. 7103-A4-SC
Summerhill Homes
2 Venture, Suite 360
Irvine, California 92618
Attention:Mr. Kevin Doherty
Subject:Supplemental Geotechnical Recommendations, Walls and BMP Basins,
Daylight Lines, Proposed Aviara Apartments, Laurel Tree Lane at Aviara
Parkway, Carlsbad, San Diego County, California
References:1. “Re: CT 2018-0002 Laurel Tree Carlsbad,” letter dated May 21, 2018, by City of Carlsbad.
2. “Tentative Map No. CT2018-0002,” various scales, 11 sheets, plotted April 18, 2018, by
REC Consultants, Inc.
3. “Revised Infiltration Recommendations, West Portion of APN 212-040-56-00, West of
Laurel Tree Lane at Aviara Parkway, Carlsbad, San Diego County, California,”
W.O. 7103-A1-SC, dated May 16, 2017, by GeoSoils, Inc.
4. “Preliminary Geotechnical Evaluation, 9.2 Acres, APN 212-040-56-00, Laurel Tree Lane at
Aviara Parkway, Carlsbad, San Diego County, California,” W.O. 7102-A-SC, dated
July 7, 2016, by GeoSoils, Inc.
Dear Mr. Doherty:
In accordance with your request and authorization, GeoSoils, Inc. (GSI), presents the
following supplemental recommendations regarding the project plans. The scope of our
services has included a review of the reference documents, analysis of data, and
preparation of this summary letter. Unless specifically superceded herein, the conclusions
and recommendations in the referenced GSI documents remain pertinent and applicable,
and should be appropriately implemented during planning, design, and construction.
As indicated in Reference No. 1, and as shown on the detail on sheet 9, the City has voiced
concern regarding the presence of a vertical cut adjoining “un-compacted fill” in the BMP
basins. With regard to the daylight line, it appears satisfactory, as shown on the referenced
plans. The following recommendations are provided to mitigate the vertical cut condition
in the BMP basins.
GeoSoils, Inc.
Summerhill Homes W.O. 7103-A4-SC
Aviara Apartments, Carlsbad July 11, 2018
File:e:\wp12\7100\7103a4.sgr Page 2
The impermeable liner needs to extend upward, past the high water mark, and into the
slope, and wrapped downward. Retaining walls should be constructed at the location of
the “Amended Soil” and natural ground. A reduced bearing value of 1,500 psf appears
warranted in the retaining wall design; and, the unit weight of water, 62.4 pcf, should be
added to the equivalent fluid pressures provided in the GSI report (horizontal pressures
table on page 42), since the retaining walls will be undrained. An increase in maximum
allowable bearing value for retaining wall footing width may also be used. The increase
should be limited to 100 psf for each additional foot of width to a maximum allowable
bearing of 2,500 psf. Passive earth pressure may be computed as an equivalent fluid
having a density of 175 pcf, with a maximum earth pressure of 2,000 psf for footings
founded into properly engineered fill or approved bedrock. The designer should specify
if import or native soils will be used for backfill. Retaining walls shown on the regional
standard drawings may not be sufficient for the above parameters. The footing should
extend a minimum of 18 inches below the gravel layer shown on the detail. Egress pipes
for all BMP basins should be backfilled with a two-sack mix of slurry.
GeoSoils, Inc.
Summerhill Homes W.O. 7103-A4-SC
Aviara Apartments, Carlsbad July 11, 2018
File:e:\wp12\7100\7103a4.sgr Page 3
If you have any questions or comments regarding this letter, please do not hesitate to
contact the undersigned.
Respectfully submitted,
GeoSoils, Inc.
John P. Franklin David W. Skelly
Engineering Geologist, CEG 1340 Civil Engineer, RCE 47857
JPF/DWS/jh
Distribution:(1) Addressee (via email)
(2) REC Consulting, Inc., Attention: Mr. Raab Rydeen (via email and US mail)
- wet signed
Appendix E.3
Infiltration Recommendations
Appendix E.4
Geotechnical Considerations
Regarding Raised Site
Elevations
Geotechnical C Geologic C Coastal C Environmental
5741 Palmer Way C Carlsbad, California 92010 C (760) 438-3155 C FAX (760) 931-0915 C www.geosoilsinc.com
March 26, 2018
W.O. 7103-A2-SC
Summerhill Homes
2 Venture, Suite 360
Irvine, California 92618
Attention:Mr. Kevin Doherty
Subject:Geotechnical Considerations Regarding Raised Site Elevations, Aviara
Parkway, 6145 Laurel Tree Road (East and West), Carlsbad, San Diego
County, California 92011
References:1. “Tentative Map for Aviara Parkway, 6145 Laurel Tree Road, Carlsbad, CA 92011,” various
scales, 11 sheets, dated January, 11, 2018, by REC Consultants, Inc.
2. “Revised Infiltration Recommendations, West Portion of APN 212-040-56-00, West of
Laurel Tree Lane at Aviara Parkway, Carlsbad, San Diego County, Califorina,” W.O. 7103-A1-
SC, dated May 16, 2017, by GeoSoils, Inc.
3. “Preliminary Geotechnical Evaluation, 9.2 Acres, APN 212-040-56-00, Laurel Tree Lane at
Aviara Parkway, Carlsbad, San Diego County, California,” W.O. 7102-A-SC, dated
July 7, 2016, by GeoSoils, Inc.
4. “Engineering Standards, Volume 5, Carlsbad BMP Design Manual (Post Construction
Treatment BMPS),” dated February 16, 2016, by City of Carlsbad.
Dear Mr. Doherty:
In accordance with your request and authorization, and as discussed with Ms. Angie Ortiz
with REC Consultants, Inc. (REC) and Sara Fernandez with KTGY Architecture and
Planning, GeoSoils, Inc. (GSI) is providing these geotechnical considerations regarding
the feasability of raising elevations at the subject site. The scope of services has included
a review of the referenced documents, analysis of data and the preparation of this report.
Unless specifically superceded herein, the conclusions and recommendations provided
in Reference 2 and 3 are still considered valid and applicable, except as specifically
modified herein, and should be appropriately implemented during the balance of project
design and construction.
CURRENTLY PROPOSED SITE ELEVATIONS
Based on a review of the tentative grading plans by REC (see Reference No.1) existing site
elevations in the western parcel are currently proposed to generally be raised from
approximately 86 feet to about 91 feet, for an over all increase of about 5 feet. Existing
GeoSoils, Inc.
Summerhill Homes W.O. 7103-A2-SC
Laurel Tree Lane, Carlsbad March 26, 2018
File:e:\wp12\7100\7103a2.gcr Page 2
elevations in the eastern parcel are proposed to be raised from approximately 94 feet to
about 100 feet, for an overall increase of about 6 feet. Current proposed infiltration
elevations for biofiltration basins ranges from about 84 to 87 feet (REC, 2018).
DISCUSSION
As indicated in References 2 and 3, groundwater (perched on bedrock), has been as high
as an elevation of about ±78 feet. It is anticipated that landscape watering and infiltration
will have the potential to raise the high perched groundwater elevation to as high as about
84 to 87 feet.
GEOTECHNICAL CONSIDERATIONS REGARDING ELEVATING PADS
Based on our review of the reference documents and our experience at the site and sites
in the vicinity, GSI recommends that the following be considered in support of raising pad
elevations:
•This would decrease the potential for perched groundwater conditions to manifest
and impact utility trenches, and the transmission of water vapor through the
foundations, potentially causing distress to building components, and/or settlement
or saturation of backfill, leading to backfill settlement/yielding, and associated
distress.
•This would make building foundations and underground utilities less susceptible to
the potentially damaging effects of corrosion and expansive soils.
•Decrease the frequency of a 100-year floods impacting site improvements (which
may occur in quick succession).
•Increase the fall of the sewer lines, which would increase the flow rate and lower the
probability of blockage.
LIMITATIONS
The conclusions and recommendations are professional opinions. These opinions have
been derived in accordance with current standards of practice, and no warranty, either
express or implied, is given. Standards of practice are subject to change with time.
GSI assumes no responsibility or liability for work or testing performed by others, or their
inaction; or work performed when GSI is not requested to be onsite, to evaluate if our
recommendations have been properly implemented. Use of this report constitutes an
agreement and consent by the user to all the limitations outlined above, notwithstanding
GeoSoils, Inc.
Summerhill Homes W.O. 7103-A2-SC
Laurel Tree Lane, Carlsbad March 26, 2018
File:e:\wp12\7100\7103a2.gcr Page 3
any other agreements that may be in place. In addition, this report may be subject to
review by the controlling authorities. Thus, this report brings to completion our scope of
services for this portion of the project.
If you have any questions or comments regarding this letter, please do not hesitate to
contact the undersigned.
Respectfully submitted,
GeoSoils, Inc.
John P. Franklin David W. Skelly
Engineering Geologist, CEG 1340 Civil Engineer, RCE 47857
CWP/JPF/DWS/jh
Distribution:(1) Addressee (via email)
(2) REC Consulting, Inc., Attention: Ms. Angie Ortiz, PE (via email and
US mail) - wet signed
Appendix E.5
Slope Analysis
SLOPE
ANALYSIS MAP AVIARA PARKWAYCANNON ROA
D
F
A
R
A
D
A
Y
AVE
PALOMAR
OAKS
WAY
COLLEGEBLVD
POIN
T
S
E
T
TI
A
AVE CAMINOREALEL