HomeMy WebLinkAboutCT 2018-0004; THE SEAGLASS; Geotechnical Update for The Seaglass; 2018-05-31GEOTECHNICAL UPDATE
FOR “THE SEAGLASS”
2646 STATE STREET
CARLSBAD, CALIFORNIA 92008
FOR
CARLSBAD VILLAGE DEVELOPMENT, LLC.
5160 CAROLL CANYON ROAD, SUITE 200
SAN DIEGO, CALIFORNIA 92121
W.O. 7452-A-SC MAY 31, 2018
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
May 31, 2018
W.O. 7452-A-SC
Carlsbad Village Development, LLC
5160 Carrol Canyon Road, Suite 200
San Diego, California 92121
Attention:Mr. Michael Akavan
Subject:Geotechnical Update for “The Seaglass,” 2646 State Street, Carlsbad,
California 92008
Dear Mr. Akavan:
In accordance with your request and authorization, GeoSoils, Inc. (GSI) has prepared the
following update of geotechnical work for the site, with respect to the governing building
Code (2016 Edition of the California Building Code [{2016 CBC}, California Building
Standards Commission {CBSC}, 2016a]) for this project, the civil plans prepared by Pasco
Laret Suiter & Associates (PLSA, 2018), and the architectural plans prepared by Safdie
Rabines Architects (SRA, 2018). See Appendix A for the referenced reports, plans and
drawings. GSI’s scope of services included a review of the referenced reports/plans,
review and response to geotechnical issues presented in a “1 Review for CT 2018-0004,”st
prepared by the City of Carlsbad (City, 2018), engineering and geologic analysis, and
preparation of this update report. Unless specifically superceded in the text of this report,
the conclusions and recommendations presented in our preliminary geotechnical
evaluation (GSI, 2015) are considered valid and applicable with respect to improvement
of the subject site, and should be properly incorporated into the design and construction
phases of site development.
SITE DESCRIPTION/PROPOSED DEVELOPMENT
The subject site consists of a rectangular shaped, vacant property located on the northeast
side of State Street, midway between the intersections of Beech Avenue and State Street,
and Laguna Avenue and State Street, in Carlsbad, San Diego County, California (see
Figure 1, Site Location Map). The property is bounded by State Street to the northeast,
and existing mobile home park to the northwest, and commercial/residential property to
the southwest. Topographically, the site is relatively flat lying, at an approximate elevation
of about 36 to 38 feet (MSL), according to a topographical plan prepared by K & S
Engineering (K&S, 2018). Site drainage appears to be directed toward State Street and
the southern property line, via sheet flow. Vegetation consists of scattered gasses, and a
large tree, located at the rear (northeast) end of the site.
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Existing improvements consist of a small, single-family residential structure, located within
the central portion of the site. A low height masonry wall is located along the northwestern
and northeastern property line, with an existing commercial building located within the
adjacent property to the south-southeast, situated along the southeast property line.
Based on our review of architectural drawings prepared by SRA (2018), development will
consist of site preparation for the construction of a four-level, multi-family residential
structure, with parking and living areas at the ground floor, with three (3) floors of
residential above. Other improvements, consisting of an elevator, exterior
parking/driveway, and typical residential landscaping are also planned. It is our
understanding, from a review of PLS (2018), that permeable traffic pavements are also
planned. Proposed improvement is shown on the Geotechnical Map (Figure 2), which
uses the Tentative Map, prepared by PLS (2018), as a base.
PREVIOUS WORK
A preliminary geotechnical evaluation of the site was performed by GSI (2015), with respect
to a previous design concept, consisting of a below-grade parking structure, with four
levels of residential above. Site work was completed with a hollow stem auger drill rig, with
soil samples collected and evaluated to develop geotechnical design parameters and
conclusions/recommendations regarding the previous development concept. The general
finding of the preliminary report, including revisions with respect to the currently planned
site development, and Code, are presented as follows:
1.In general, the site may be characterized as being mantled by a thin veneer of
undifferentiated, Quaternary-age colluvium and undocumented fill. These surficial
earth units are immediately underlain by Quaternary-age old paralic deposits
(formerly termed “terrace deposits”) extending to depths on the order of 10 to
12 feet below the existing grades. Below these depths, Eocene-age sedimentary
bedrock, belonging to the Santiago Formation occurs.
2.Due to their relatively low density and lack of uniformity, all surficial deposits of
colluvium, undocumented fill, and potentially near surface weathered old paralic
deposits, are considered unsuitable for the support of settlement-sensitive
improvements (i.e., foundations, concrete slab-on-grade floors, site walls, exterior
hardscape, etc.) and/or planned fills in their existing state. Based on the available
data, the thickness of these soils across the site is anticipated to be on the order of
2 feet to 4 feet. However, localized thicker sections of unsuitable soils cannot be
precluded, and should be anticipated. Conversely, the underlying unweathered old
paralic deposits (previously referred to as “terrace deposits”) and
Santiago Formation (at depth) are generally considered suitable for the
support of settlement-sensitive improvements and/or engineered fill.
Undercutting/overexcavation of paralic deposits will be necessary for support of
ground floor portions of the structure. Slot cuts should be anticipated in order to
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complete remedial removals and overexcavation adjacent to settlement-sensitive
improvements to remain.
•GSI anticipates that due to the nature of the subsurface earth materials and the
location of adjacent developments/improvements, the completion of remedial
grading about the perimeter of the site will likely require slot cuts to complete the
installation and construction.
•GSI has considered the design alternatives including isolated spread/continuous
footings and mat foundations for support of the proposed building upon a
recompacted fill subgrade. Site soils are expansive and should be considered in
foundation design and construction.
•The 2016 CBC (CBSC, 2016a) indicates that removals of unsuitable soils be
performed across all areas to be graded, under the purview of the grading permit,
not just within the influence of the proposed building. 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. Thus, any settlement-sensitive improvements (walls,
curbs, flatwork, etc.), constructed within this zone may require deepened
foundations, reinforcement, etc., or will retain some potential for settlement and
associated distress. This will also require proper disclosure to any owners and all
interested/affected parties should this condition exist at the conclusion of grading.
•Expansion Index (E.I.), and plasticity index (P.I.) testing performed on representative
samples of the onsite soil indicates E.I.s ranging from less than 20 (very low
expansive) to 73 (medium expansive), and a P.I. of up to 26. As such, some site soil
(primarily the upper portion of old paralic deposits) meet the criteria of expansive
soils as defined in Section 1803.5.3 of the 2016 CBC. Soil expansivity should be
re-evaluated at the conclusion of grading and updated data for final foundation
design provided.
•Corrosion testing performed on a representative sample of the onsite soils indicates
site soils are mildly alkaline with respect to soil acidity/alkalinity; are corrosive to
severely corrosive to exposed buried metals when saturated; present negligible to
moderate sulfate exposure to concrete (per ACI 318-14): and contain low
concentrations of soluble chlorides. It should be noted that GSI does not consult
in the field of corrosion engineering. Thus, the client, project architect, and project
structural engineer should agree on the level of corrosion protection required for the
project and seek consultation from a qualified corrosion consultant as warranted,
especially in light of the site’s proximity to the Pacific Ocean, which is a corrosive
environment, and the potential for water to perch within earth materials with
contrasting permeabilities and/or densities.
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•A perched groundwater table was encountered at depths of approximately 12 feet
below existing surface grades onsite. Based on a review of ground surface
elevations provided on K&S (2018), this equates to an approximate elevation of
about 25 feet MSL. Groundwater is not anticipated to significantly affect the
proposed development. However, the perched groundwater table may present
difficulties in the form of caving soils, and/or seepage during excavations for any
deep underground utilities, if completed in proximity of the elevations noted above.
The need for dewatering cannot entirely be precluded. Perched water may also
occur in the future along zones of contrasting permeabilities and/or density, if the
site is subject to rainfall of a significant intensity and duration, during and after
construction. This potential should be disclosed to all interested/affected parties.
•The potential for below-grade moisture around the elevator pit will likely require a
permanent sump. Moisture vapor control in the garage slab will reduce
transmission of water vapor and the potential for moisture to damage storage,
equipment, or vehicles.
•GSI (2015) indicates that there are no known active faults crossing the site and the
natural slope upon which the site is located has a very low susceptibility to
deep-seated landslides. Owing to the depth to groundwater and the dense nature
of the old paralic deposits and underlying Santiago Formation, the potential for the
site to be adversely affected by liquefaction/lateral spreading is considered very low.
Site soils are considered erosive. Thus, properly designed site drainage is
necessary in reducing erosion damage to the planned improvements.
•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 structure will be repairable in the event of the design seismic event. This
potential should be disclosed to any owners and all interested/affected parties.
•Additional adverse geologic features that would preclude project feasibility were not
encountered, based on the available data.
Unless specifically superceded herein, the conclusions and recommendations presented
in GSI (2015) remain valid and applicable.
GeoSoils, Inc.
Carlsbad Village Development, LLC W.O. 7452-A-SC
2646 State Street, Carlsbad May 31, 2018
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UPDATED SEISMIC DESIGN
General
It is important to keep in perspective that in the event of an upper bound (maximum
probable) or credible earthquake occurring on any of the nearby major faults, strong
ground shaking would occur in the subject site's general area. Potential damage to any
structure(s) would likely be greatest from the vibrations and impelling force caused by the
inertia of a structure's mass than from those induced by the hazards listed above. This
potential would be no greater than that for other existing structures and improvements in
the immediate vicinity.
Seismic Shaking Parameters
Based on the site conditions, the following table summarizes the updated site-specific
design criteria obtained from the 2016 CBC (CBSC, 2016a), Chapter 16 Structural Design,
Section 1613, Earthquake Loads. The computer program “U.S. Seismic Design Maps,
provided by the United States Geologic Survey (USGS, 2013 [updated 2014]) was utilized
for design (http://geohazards.usgs.gov/designmaps/us/application.php). The short
spectral response utilizes a period of 0.2 seconds.
2016 CBC SEISMIC DESIGN PARAMETERS
PARAMETER VALUE 2016 CBC
REFERENCE
Risk Category II Table 1604.5
Site Class D Section 1613.3.2/ASCE 7-10
(p. 203-205)
sSpectral Response - (0.2 sec), S 0.822 g Section 1613.3.1
Figure 1613.3.1(1)
1Spectral Response - (1 sec), S 0.317 g Section 1613.3.1
Figure 1613.3.1(2)
aSite Coefficient, F 1.171 Table 1613.3.3(1)
vSite Coefficient, F 1.765 Table 1613.3.3(2)
Maximum Considered Earthquake Spectral
MSResponse Acceleration (0.2 sec), S 0.963 g Section 1613.3.3
(Eqn 16-37)
Maximum Considered Earthquake Spectral
M1Response Acceleration (1 sec), S 0.560 g Section 1613.3.3
(Eqn 16-38)
5% Damped Design Spectral Response
DSAcceleration (0.2 sec), S 0.642 g Section 1613.3.4
(Eqn 16-39)
5% Damped Design Spectral Response
D1Acceleration (1 sec), S 0.373 g Section 1613.3.4
(Eqn 16-40)
GeoSoils, Inc.
2016 CBC SEISMIC DESIGN PARAMETERS
PARAMETER VALUE 2016 CBC
REFERENCE
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MPGA - Probabilistic Vertical Ground Acceleration may
be assumed as about 50% of these values. 0.377 g ASCE 7-10 (Eqn 11.8.1)
Seismic Design Category D Section 1613.3.5/ASCE 7-10
(Table 11.6-1 or 11.6-2)
GENERAL SEISMIC PARAMETERS
PARAMETER VALUE
Distance to Seismic Source (Rose Canyon fault)about 11.8 mi (19.0 km)(1)
WUpper Bound Earthquake (Rose Canyon fault)M = 7.2(2)
- From Blake (2000)(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 2016 CBC (CBSC, 2016a) 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.
PRELIMINARY CONCLUSIONS AND RECOMMENDATIONS
Based on our current and previous site work, and geotechnical engineering analysis, and
a review of work by others, it is our opinion that the site appears suitable for the proposed
development from a geotechnical engineering and geologic viewpoint, provided that the
recommendations presented herein, are incorporated into the design and construction
phases of site development.
EARTHWORK
General
All grading should conform to the guidelines presented in the 2016 CBC (CBSC, 2016a),
the City, and as recommended herein. When code references are not equivalent, the more
stringent code should be followed. During earthwork construction, all site preparation and
the general grading procedures of the contractor should be observed and the fill
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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.
Future Plan Grading
Cut and fill grading techniques are anticipated in order to bring the site to the desired
grades for building pad construction. Based on a review of PLA (2018), plan grades are
anticipated to generally approximate existing grades, with maximum plan cuts and fills on
the order of about 2 feet, or less, are anticipated. As such, the bulk of grading is
anticipated to consist of “remedial” earthwork. Significant graded slopes are not
anticipated.
Preliminary Earthwork Factors (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:
Quaternary Colluvium/Undocumented Fill ..................10% to 15% shrinkage
Quaternary Old Paralic Deposits..............................0% to 5% bulking
It should be noted that the above factors are estimates only, based on preliminary data.
Colluvium/disturbed natural ground may achieve higher shrinkage if organics or clay
content is higher than anticipated. Further, bulking estimates for old paralic deposits may
be less than indicated above depending on the degree of weathering. 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. If the Client requires
additional information regarding embankment factors, additional studies could be provided
upon request.
Demolition/Grubbing
1.Vegetation and any miscellaneous debris should be removed from the areas of
proposed grading.
2.Any existing subsurface structures uncovered during the recommended remedial
earthwork should be observed by GSI so that appropriate remedial
recommendations can be provided.
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3.Cavities or loose soils remaining after demolition and site clearance should be
cleaned out and observed by the soil engineer. The cavities should be replaced
with a 2- to 3-sack sand-cement slurry or fill materials that have been moisture
conditioned to at least optimum moisture content and compacted to at least
95 percent of the laboratory standard (ASTM D 1557).
4.Onsite septic systems (if encountered) should be removed in accordance with
San Diego County Department of Environmental Health (DEH)
standards/guidelines.
5.Existing, abandoned wells should be destroyed in accordance with DEH
standards/guidelines.
Treatment of Existing Ground/Remedial Grading
1.Remedial grading shall consist of all surficial colluvium, undocumented fill, and any
weathered old paralic deposits (if present) to encounter the suitable, dense
unweathered old paralic deposits (the depth to the Santiago Formation is
considered to be greater than the necessary removal, and/or overexcavation
depths). Based on the available subsurface data (GSI, 2015), the depth of remedial
grading excavations are anticipated to be on the order of 2 to 4 feet below the
existing grades. Removed soils may be re-used in engineered fills, provided that
the soil is cleaned of any deleterious material and moisture conditioned, and
compacted to a minimum 95 percent relative compaction (ASTM D 1557). Remedial
grading should be completed throughout the entire property.
2.Remedial grading may utilize alternating (“A’, “B,” and “C”) slot excavations
adjacent to any settlement sensitive improvements (walls, building, etc.) to remain
about the perimeter of the site. A maximum slot cut width of 8 feet may be
considered, on a preliminary basis.
3.Subsequent to the above, remedial excavations, should be scarified to a depth of
at least 8 inches, brought to at least optimum moisture content, and recompacted
to a minimum relative compaction of 90 percent of the laboratory standard (ASTM
D 1557), prior to any fill placement.
4.Localized deeper remedial grading excavations may be necessary due to buried
drainage channel meanders or dry porous materials, septic systems, etc. The
project geotechnical consultant should observe all remedial grading excavations
during earthwork construction. If deeper removals are needed, below the designed
height of the adjacent shoring, a slot cut approach may be used to reduce the
potential for excessive shoring deflection.
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Overexcavation
In order to provide for the uniform support of the structure, and reduce the potential for
damaging differential settlement, GSI recommends that the ground floor of the structure
is undercut to provide at least 2 feet of compacted fill beneath the foundation system.
Based on a 24- to 30-inch deep footing, the depth of undercut should be on the order of
4 to 4½ feet below existing grades. A deeper overexcavation will be necessary in the
vicinity of the elevator well. Following overexcavation, the exposed subsoils should be
scarified to a depth of at least 12 inches, moisture conditioned to at least optimum moisture
content and then be recompacted to at least 90 percent of the laboratory standard (ASTM
D 1557). The overexcavation may then be backfilled with the excavated earth materials
that have been placed in relatively thin (i.e., approximately 8- to 10-inch thick) lifts, moisture
conditioned to at least 1 to 2 percent above the soils optimum moisture content, and
compacted to at least 90 percent of the laboratory standard (ASTM D 1557) with vibratory
compaction equipment.
Fill Placement
Subsequent to ground preparation, any required fill materials should be brought to at least
1 to 2 percent above the soils optimum moisture content, placed in thin 6- to 8-inch lifts,
and mechanically compacted to obtain a minimum relative compaction of 90 percent of the
laboratory standard (ASTM D 1557). Fill materials should not be greater than 12 inches
in any dimension. Underground-utility agencies/companies may have stricter requirements
with respect to the particles sizes of backfill placed in utility trenches.
Subdrains
Given the relatively flat lying conditions across the site, a gravity flow system at street level
may be provided by finished grading design. Any below grade portion of the structure,
such as an elevator well, will need to have flow collected, tight-lined, and utilize a sump
pump, to direct the water to the street. Walls below grade will need to be “waterproofed.”
Temporary Slopes
Unsupported temporary excavation walls ranging between 4 and 20 feet in gross overall
height may be constructed in accordance with CAL-OSHA guidelines for Type “B” soils
(i.e., 1:1 [h:v] slope), provided that groundwater and/or running sands are not exposed.
Should such conditions be exposed, temporary slopes should be constructed in
accordance with CAL-OSHA guidelines for Type “C” soils (i.e., 1½:1 [h:v] 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 may
be necessary if adverse conditions are observed. If temporary slopes conflict with property
boundaries or other boundary restrictions, shoring or alternating slot excavations may be
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necessary. The need for shoring or alternating slot excavations could be further evaluated
during grading plan review stage. Soil and building materials and heavy construction
equipment should not be stockpiled, stored, nor operated within “H” feet from the top of
temporary excavations walls where “H” equals the height of the excavation wall.
Import Fill Materials
All import fill material should be tested by GSI prior to placement within the site. GSI would
also request environmental documentation (e.g., Phase I Environmental Site Assessment)
pertaining to proposed export site, to evaluate if the proposed import could present an
environmental risk to the planned development. At least five (5) business days of lead time
will be necessary for the required laboratory testing and document review.
FOUNDATION DESIGN AND CONSTRUCTION
Preliminary recommendations for foundation design and construction are provided in the
following sections. These preliminary recommendations have been developed from our
understanding of the currently planned site development, site observations, work by others
(see Appendix A), and engineering analyses. Foundation design should be re-evaluated
at the conclusion of site grading/remedial earthwork for the as-graded soil conditions.
Although not anticipated, revisions to these recommendations may be necessary. 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 residential structures
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.
The information and recommendations presented in this section are not meant to
supercede design by the project structural engineer or civil engineer specializing in
structural design. Upon request, GSI could provide additional input/consultation regarding
soil parameters, as related to foundation design.
In the following sections, GSI provides preliminary design and construction
recommendations for foundations underlain by detrimentally expansive soil conditions.
Foundation systems constructed within the influence of detrimentally expansive soils (i.e.,
E.I. > 20 and P.I. > 15) will require specific design to resist expansive soil effects per
Sections 1808.6.1 or 1808.6.2 of the 2016 CBC.
Foundations in Consideration of Expansive and Corrosive Soils
GSI (2015) indicates that medium expansive soils (E.I.s greater than 50) exist onsite.
Where building areas are underlain by expansive soils, as defined in Section 1803.5.3 of
the 2016 CBC (CBSC, 2016a), foundations will also require specific design by the structural
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engineer to mitigate expansive soil effects as required in Sections 1808.6.1 or 1808.6.2 of
the 2016 CBC (CBSC, 2016a). These foundation types generally include mat slabs
(WRI, 1996), or post-tension slab foundations (PTI; 2014, 2013, 2012). Recommendations
for “PT” slab foundations are provided herein.
Corrosion evaluations prepared in preparation of GSI (2015) indicate that the tested
samples of the onsite soils are moderately alkaline with respect to soil acidity/alkalinity; are
corrosive to exposed, buried metals when saturated; present negligible, to moderate
sulfate exposure to concrete (per Table 19.3.1.1 of ACI 318R-14); and have low chloride
content. It should be noted that GSI does not consult in the field of corrosion engineering.
Thus, the client, project architect, and project structural engineer should agree on the level
of corrosion protection required for the project and seek consultation from a qualified
corrosion consultant as warranted, especially in light of the site’s proximity to the Pacific
Ocean, which is a corrosive environment. It should be noted that sulfate levels indicate a
sulfate exposure Class S1, and a moderate corrosion exposure class of C1 (concrete will
be exposed to moisture), per Tables 19.3.1.1 and 19.3.2.1 of ACI 318R-14 (ACI, 2014).
As with all grading projects, additional expansion and corrosive soil evaluations would be
recommended at the completion of precise earthwork. On a preliminary basis, reinforced
concrete mix design for foundations, slab-on-grade floors, and pavements should also
conform to “Exposure Class C1” in Tables 19.3.1.1 and 19.3.2.1 of ACI 318R-14, as
concrete would likely be exposed to moisture.
PRELIMINARY RECOMMENDATIONS - FOUNDATIONS
General
Preliminary recommendations for foundation design and construction are provided in the
following sections. These preliminary recommendations have been developed from our
understanding of the currently planned site development, site observations, subsurface
exploration, laboratory testing, and engineering analyses. Foundation design should be
re-evaluated at the conclusion of site grading/remedial earthwork for the as-graded soil
conditions. Although not anticipated, revisions to these recommendations may be
necessary. 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
additions 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.
The information and recommendations presented in this section are not meant to
supercede design by the project structural engineer or civil engineer specializing in
structural design. Upon request, GSI could provide additional input/consultation regarding
soil parameters, as related to foundation design.
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GSI understands that the project is in its very conceptual stages. Thus, the foundation
design recommendations, included herein, are based on anticipated average and
maximum static column loads of 100 and 250 kips, respectively. Maximum wall loads are
anticipated to be on the order of 5 kips per lineal foot. The slabs-on-grade are anticipated
to have typical car and light loads on the order of 50 to 200 psf. It is unknown if equipment
and elevator pit areas will be included in the design. GSI does not anticipate high vibratory
equipment loads on the floor slabs. GSI also does not anticipate highly sensitive electrical
equipment mounted on the floor slab. The lowest finish grade is anticipated to be at a
elevation of about 38 to 40 feet MSL.
Based on the above, we have considered the following design alternatives:
C Isolated spread/continuous footings (i.e., conventional).
C Mat foundation
The foundation design recommendation contained in this report may be modified once
actual loading conditions have been provided for GSI review. All foundations should be
designed using at a minimum, the parameters and static settlements described herein. All
foundations should be evaluated for seismic deformations described herein
Expansive Soils
Current laboratory testing indicates that the onsite soils exhibit expansion index(E.I.) values
ranging on the order of less than 20 to 73 (very low to medium), with a plasticity index (P.I.)
for medium expansive soils evaluated as 26. As such, some site soil meets the criteria of
detrimentally expansive soils as defined in Section 1803.5.3 of the 2016 CBC. Foundation
systems constructed within the influence of detrimentally expansive soils (i.e., E.I. > 20 and
P.I. > 15) will require specific design to resist expansive soil effects per Sections 1808.6.1
or 1808.6.2 of the 2016 CBC, and should be reviewed by the project structural engineer.
Preliminary Conventional Foundation Design
The following foundation construction recommendations are presented as a minimum
criteria from a soils engineering viewpoint, where the planned improvements are underlain
by at least 7 feet of non-detrimentally expansive soils (i.e., E.I.<21 and P.I. <15). Should
foundations be underlain by (detrimentally) expansive soils, as is anticipated for the ground
floor portions of the structure, they will require specific design to mitigate expansive soil
effects as required in Sections 1808.6.1 or 1808.6.2 of the 2016 CBC.
1.Conventional foundation systems should be designed and constructed in
accordance with guidelines presented in the 2016 CBC (CBSC, 2016a).
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2.Based on the anticipated foundation loads and preliminary design information
provided us, it is our opinion that the proposed structure could be favorably
supported on a minimum 2-foot thick layer of engineered fill, compacted to at least
95 percent of the laboratory standard (ASTM D 1557), overlying dense,
unweathered old paralic deposits. Building loads may be supported on continuous
or isolated spread footings designed in accordance with the following
recommendations.
ALLOWABLE BEARING VALUES FOR FOOTINGS
DEPTH BELOW LOWEST
ADJACENT FINISHED
GRADE (INCHES)
ALLOWABLE BEARING
CAPACITY FOR
SPREAD FOOTINGS
(MINIMUM WIDTH = 4 FEET)
ALLOWABLE BEARING
CAPACITY FOR CONTINUOUS
WALL FOOTINGS
(MINIMUM WIDTH = 2 FEET)
30 to 36 2.5 ksf 2.5 ksf
48 3.0 ksf 3.0 ksf
The above values are for dead plus live loads and may be increased by one-third
for short-term wind or seismic loads. Where column or wall spacings are less than
twice the width of the footing, some reduction in bearing capacity may be necessary
to compensate for the effects of footings with shared bearing soils. GSI should
review the foundation plans and overlying building load patterns and evaluate this
potential with the structural consultant. Reinforcement should be designed in
accordance with local codes and structural considerations.
The recommended allowable bearing capacity provided herein is generally based
on maximum static total and differential settlements of up to 2 inches and 1 inch,
respectively. Differential settlements are over a distance of 50 lateral feet or
between heaviest and lightest foundation loads. Actual settlement can be estimated
on the basis that settlement is roughly proportional to the net contact bearing
pressure on compacted fill, or formation. The majority of the settlement should
occur during construction as building loads are applied. Since settlement is a
function of footing size and contact bearing pressure, some static differential
settlement can be expected between adjacent columns or walls where a large
differential loading condition exists. However, for most cases, differential
settlements are considered unlikely to exceed 1¼ inches in 50 feet (angular
distortion = 1/480). With increased footing depth/width ratios, differential settlement
should be less. The anticipated total vertical deformation (post-earthquake) for the
design seismic event may be on the order of ±1 inch with a potential seismic
differential settlement of approximately ¼ inch to ¾ inch over 50 feet horizontally
(i.e., angular distortion approximately 1/800) under the basement/garage structure.
Other settlement-sensitive improvements (i.e., underground utilities, pavements,
flatwork) are susceptible to seismic settlement outside the footprint of the
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basement/garage structure. These evaluations have assumed a local control of
groundwater around the foundation.
3.Foundation embedment depth excludes concrete slabs-on-grade, and/or slab
underlayment. Foundations for the ground level structure should bear entirely on
a minimum 2-foot thick layer of approved engineered fill overlying unweathered,
dense old paralic deposits (i.e., beneath the bottom of the footing). All isolated pad
footings should be tied to the perimeter foundation in at least one direction to
reduce the potential for lateral drift.
4.For foundations deriving passive resistance from engineered fill, prepared in
accordance with the recommendations provided in this report, a pressure of 250 pcf
may be used if the footing face is embedded entirely in engineered fill, and the
embedment is 24 to 48 inches. For footings embedded entirely into dense,
unweathered old paralic deposits or Santiago Formation, a passive resistance value
of 300 pcf may be used.
5.The upper 6 inches of passive pressure should be neglected if not confined by
slabs or pavement.
6.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.
7.When combining passive pressure and frictional resistance, the passive pressure
component should be reduced by one-third.
8.Although not anticipated, given our understanding of the proposed development,
all footing setbacks from slopes should comply with Figure 1808.7.1 of the
2016 CBC. GSI recommends a minimum horizontal setback distance of 7 feet as
measured from the bottom, outboard edge of the footing to the slope face.
Foundations should also extend below a 1:1 (h:v) projection up from the bottom
outside edge of remedial grading excavations.
9.Footings for structures adjacent to retaining/privacy walls should be deepened so
as to extend below a 1:1 projection from the heel of the wall. Alternatively, walls
may be designed to accommodate structural loads from buildings or appurtenances
as described in the “Retaining Wall” section of this report.
10.Footings constructed below a 1:1 projection from adjacent property lines should be
designed for any applicable surcharge.
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PRELIMINARY CONVENTIONAL FOUNDATION
CONSTRUCTION RECOMMENDATIONS
Current laboratory testing indicates that some onsite soils meet the criteria of detrimentally
expansive soils as defined in Section 1803.5.3 of the 2016 CBC. The following foundation
construction recommendations are presented as a minimum criteria from a soils
engineering viewpoint, where the planned improvements are underlain by at least 7 feet,
and perhaps more (as determined during grading), of non-detrimentally expansive soils
(i.e., E.I.<21 and P.I. <15). Should foundations be underlain by expansive soils, such as
is anticipated for the ground floor portions of the structure, they will require specific design
to mitigate expansive soil effects as required in Sections 1808.6.1 or 1808.6.2 of the
2016 CBC (CBSE, 2016a).
1.Exterior and interior footings should be founded into approved engineered fill, as
indicated in the previous “Preliminary Foundation Design” section of this report.
Reinforcement should be designed in accordance with local codes and structural
considerations.
2.All interior and exterior column footings, and perimeter wall footings, should be tied
together via grade beams in at least one direction. The grade beam should be at
least 24 inches square in cross section, and the base of the reinforced grade beam
should be at the same elevation as the adjoining footings. Reinforcement should
be designed in accordance with local codes and structural considerations.
3.A grade beam, reinforced as previously recommended and at least 24 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.
4.Non-vehicular slab-on-grade floors should have a minimum thickness of 5 inches
with steel reinforcement consisting of No. 3 reinforcing bars positioned at 18 inches
on center in two perpendicular directions (i.e., long axis and short axis). 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. Slab-on-grade floors intended to receive vehicular traffic
should conform to the recommendations contained in the “Preliminary
Recommendations for Portland Cement Concrete Pavements” section of this report.
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 recommendations, contained herein, are considered minimum
guidelines.
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5.Slab subgrade pre-soaking may be required for the onsite soil conditions, should
medium expansive soils be present near finish grade. If this is the case, the
subgrade soils should be moisture conditioned to 2 percent over optimum moisture
content (or 1.2 x optimum moisture, whichever is greater). This will need to be
verified within 2 hours of the placement of underlayment sand and gravel and the
vapor retarder. However, for very low to low expansive soils, the developer should
consider moisture conditioning slab subgrade materials to at least optimum
moisture content to a minimum depth of 12 inches, within 72 hours of the placement
of underlayment sand and gravel and the vapor retarder.
6.Soils generated from footing excavations to be used onsite should be compacted
to a minimum relative compaction of 95 percent of the laboratory standard
(ASTM D 1557), whether the soils are to be placed inside the foundation perimeter
or in other areas of the site. This material must not alter positive drainage patterns
that direct drainage away from the structural areas and toward the street.
7.Reinforced concrete mix design should conform to recommendations contained in
the “Soil Moisture Transmission Considerations” section of this report, and should
consider the site’s proximity to the Pacific Ocean corrosive environment, and the
elevated chloride concentrations found in some of the onsite soils.
Preliminary Mat Foundation Recommendations
Given the nature of the proposed building (i.e., podium design), estimated column loads,
the settlement potential of the underlying soils, and the proximity of a perched groundwater
table below planned grades, a mat-type foundation system should be considered in
providing foundation support for the proposed building in lieu of interconnected spread
footings and grade beams with an overlying slab-on-grade floor. A mat foundation may
consist of either reinforced uniform thickness foundation (UTF) slabs with turned down
edges or may incorporate interconnected, interior stiffening beams. The latter is commonly
referred to as a “waffle slab.” The UTF approach is typically preferred by under-slab utility
installers in order to reduce penetrations through the interior beams. UTF may be used
in the mat design if the structural consultant can demonstrate that the alternative is
equivalent to the recommended waffle slab/footings.
The structural engineer may supersede the following recommendations based on the
planned building loads and use. WRI (Wire Reinforcement Institute, 1996) methodologies
for design may be used. Reinforcement bar sizing and spacing for mat slab foundations
should be provided by the structural engineer. The parameters herein may require
modification to mitigate the effects of the estimated total and differential settlements
reported herein.
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Mat Foundation Design
The design of mat foundations should incorporate the vertical modulus of subgrade
sreaction (K ). This value is a unit value for a 1-foot square footing and should be reduced
in accordance with the following equation when used with the design of larger foundations.
This is assumes that the bearing soils will consist of a minimum 2-foot thick layer of
engineered fill, compacted to at least 95 percent of the laboratory standard (ASTM D 1557),
overlying dense, non-saturated unweathered old paralic deposits.
S where: K = unit subgrade modulus
R K = reduced subgrade modulus
B = minimum or smallest foundation width of the mat (in feet)
Mat Foundation Vertical Bearing
For a mat foundation bearing uniformly on a minimum 2-foot thick layer of engineered fill,
compacted to at least 95 percent of the laboratory standard (ASTM D 1557), overlying
dense, non-saturated unweathered old paralic deposits, a maximum allowable vertical net
bearing capacity of 2,000 psf is recommended. GSI anticipates that the bearing will very
vary from 1,500 to 2,000 psf under higher concentrated loads across the mat. This value
may be increased by one-third for short-term loads including wind or seismic and include
a factor-of-safety of 3.0 for bearing capacity.
The structural mat foundation slab should have a double mat of steel (minimum No. 5
reinforcing bars located at 12 inches on center each way, top and bottom). The thickness
of the mat foundation slab should be defined by the structural consultant but not be less
than 8 inches thick. Non-UTF mat foundations should incorporate an edge footing that is
at least 18 inches wide and minimally extends 30 inches below the lowest adjacent grade
into approved engineered fill. UTF mat embedment should be at least 24 inches below the
lowest adjacent grade into approved engineered fill. Concrete mix design and slab
underlayment recommendations are provided in the “Soil Moisture Transmission
Considerations” section of this report. Mats may be designed by ACI 318-14 and/or
WRI (1996). The need and arrangement of grade beams will be in accordance with the
structural consultant’s recommendations.
Mat Foundation Lateral Resistance
Please refer to the “Preliminary Conventional Foundation Design” section of this report for
recommendations pertaining to passive resistance and the coefficient of friction to be used
in mat foundation design.
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Subgrade Modulus and Effective Plasticity
SThe modulus of subgrade reaction (K ) and effective plasticity index (P.I.) to be used in mat
foundation design (ACI 318-14 or WRI [1996]) for the very low to medium expansive nature
of the onsite soils are presented in the following table.
VERY LOW TO LOW EXPANSION
(E.I. = 0-50)
MEDIUM EXPANSION
(E.I. = 51-90)
SS K =100 pci/inch, PI <15 K =85 pci/inch, PI = 26
Other Structural Considerations for Typical Mat-Type Foundations
In order to mitigate the effects from post-development perched water and to impede water
vapor transmission, structural mats, shall be in accordance with ACI 318-14 per the
2016 CBC (CBSC, 2016a), for low permeability concrete (i.e., a maximum water-cement
ratio of 0.50). Recommendations for slab underlayment and soil moisture transmission
considerations are presented in a later section of this report.
Nuisance cracking may be lessened by the addition of engineered reinforcing fibers in the
concrete and careful control of water/cement ratios. The use of epoxy-coated reinforcing
bars should be considered and are dependent on the structural consultant’s waterproofing
and corrosion specialists’ recommendations.
Corrosion and Concrete Mix
Preliminary testing indicates that some site soils present a moderate sulfate exposure to
concrete, per Table 19.3.1.1 of ACI 318-14 (ACI, 2014) and should be considered in the
selection of concrete type for this project. 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
GSI has evaluated the potential for vapor or water transmission through the concrete floor
slabs, in light of typical floor coverings, improvements, and use. 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
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of the type of flooring materials typically used for the particular application (State of
California, 2018). These recommendations may be exceeded or supplemented by a water
“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 E.I. test results presented herein, and 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 slab-on-grade floors, including garage slabs, should be a minimum of
5 inches thick.
•Concrete slab underlayment should consist of a 15-mil vapor retarder, or equivalent,
with all laps sealed per the 2016 CBC and the manufacturer’s recommendation.
The vapor retarder should comply with the ASTM E 1745 - Class A criteria, and be
installed in accordance with American Concrete Institute (ACI) 302.1R-04 and
ASTM E 1643. An example of a vapor retarder product that complies with
ASTM E 1745 - Class A criteria is Stego Industries, LLC’s Stego Wrap.
•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, shall 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.
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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.
•The vapor retarder should 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) placed directly on the prepared, moisture
conditioned, subgrade. The vapor retarder should be sealed to provide a
continuous retarder under the entire slab, as discussed above.
•Concrete should have a maximum water/cement ratio of 0.50. This does not
supercede Tables 19.3.1.1 and 19.3.2.1 of ACI (2014) for corrosion or other
corrosive requirements. 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 owner(s) should be specifically advised which areas are suitable for tile flooring,
vinyl flooring, or other types of water/vapor-sensitive flooring and which are not
suitable. In all planned floor areas, flooring shall be installed per the manufactures
recommendations.
•Equipment in garage or elevator pit areas may require special consideration
depending on the sensitivity to soil moisture transmission.
•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 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 foundations
or improvements. The vapor retarder contractor should have representatives onsite during
the initial installation.
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RETAINING WALLS
Current plans do not indicate the presence of significant retaining walls. If needed,
retaining wall design and construction recommendations are presented in GSI (2015).
PRELIMINARY PORTLAND CEMENT CONCRETE
PAVEMENT (PCCP) DESIGN RECOMMENDATIONS
The preliminary design for parking garage ingress/egress lane and parking garage drive
lane, and parking stall PCCP was evaluated using the pavement software PCAPAV. Our
sevaluation considered a modulus of subgrade reaction (K ) equivalent to 100 pounds per
cubic inch (pci), a modulus of rupture (MR) of 520 pounds per square inch (psi), the
absence of concrete shoulders and dowels for the parking garage ingress/egress lanes,
and the inclusion of concrete shoulders and dowels for the parking garage drive lanes, and
parking stalls. A load safety factor of 1.2 was applied to the parking garage ingress/egress
lanes and a load safety factor of 1.1 was applied to the parking garage drive lanes and
parking stalls. An average daily truck traffic (ADTT) value of 5 was also considered in our
evaluation. GSI does not practice in the field of traffic engineering. Thus, the actual ADTT
should be provided by a licensed traffic engineer or licensed civil engineer specializing in
traffic engineering. PCCP was evaluated for a 20-year design life. Based on our analysis,
the PCCP sections are provided in the following table:
PORTLAND CONCRETE CEMENT PAVEMENTS (PCCP)
TRAFFIC AREAS CONCRETE TYPE PCCP THICKNESS
Parking Garage Stalls 560-C-3250 6 inches
NOTE: All PCCP is designed as un-reinforced and bearing directly on subgrade compacted to at least
90 percent of the laboratory standard (ASTM D 1557). 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 should 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 reinforced accordingly. Concrete cut-off walls or
thickened PCCP edges should be considered where PCCP is adjacent to landscaping. The cut-off wall of
thickened edge should be at least 6 inches wide and extend at least 12 inches below the PCCP subgrade.
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 3,250 psi
Repair or replacement of any existing asphaltic concrete pavements within State Street
should be performed in accordance with City of Carlsbad standards.
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PORTLAND CEMENT CONCRETE (PCC) FLATWORK AND OTHER IMPROVEMENTS
The soil materials on site may be 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, it is important that
the developer be aware 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 non-vehicular concrete slabs should be moisture conditioned
to at least optimum moisture content and then compacted to achieve a minimum
90 percent of the laboratory standard (ASTM D 1557). Although not anticipated, if
expansive soils (E.I. > 20) are present, the subgrade should be moisture
conditioned to at least 1 to 2 percentage points above optimum moisture content
and then be compacted to achieve a minimum 90 percent of the laboratory
standard (ASTM D 1557). Concrete should be placed within 72 hours of subgrade
preparation provided there is written approval of the subgrade by the geotechnical
consultant.
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 approach slabs
should be deigned and constructed in accordance with City of Carlsbad standards.
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
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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.
5.Concrete compression strength for non-vehicular slabs, outside the building
footprint, may be a minimum of 2,500 psi.
6.Driveways, sidewalks, and patio slabs adjacent to the building should be separated
from the building 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 structurally 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 or expansive soil conditions.
11.Positive site drainage should be maintained at all times. Finish grade on the lot
should provide a minimum of 1 to 2 percent fall to the street, as indicated herein.
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 owner or owner’s association. Surface drainage in
excess of 2 percent in untreated fill soils is not recommended due to the low
plasticity and increased erosion potential.
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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ONSITE STORM WATER BMPs
A discussion of storm water treatment was presented in GSI (2015). Based on a review of
GSI (2015) the following comments are provided with respect to site soil conditions,
planned and existing improvements, civil plans (PLA, 2018), City’s BMP manual, and the
soils infiltration capabilities. Forms I-8 and I-9, from the BMP manual (City of Carlsbad,
2016), are also included herein as Appendix B.
Infiltration Rate
Based on our review of the soil survey maps and information provided by the United States
Department of Agriculture (http://websoilsurvey.sc.egov.usda.gov/App/
WebSoilSurvey.aspx), the onsite soils consist of the Marina loamy coarse sand, 2 to
9 percent slopes. The United States Department of Agriculture (USDA) indicates that the
capacity of the most limiting layer to transmit water (Ksat) for this mapped soil unit is
moderately high to high (0.57 to 1.98 inches per hour [in/hr]). The USDA also indicates
that the Hydrologic Soil Group (HSG) designation for this mapped soils unit is HSG “B,”
which is relatively amenable to infiltration. However, our site evaluation (GSI, 2015)
indicates that the site is underlain with a surficial deposit of interbedded clay, clayey sand,
and sand, overlying very dense and relatively impermeable sandstone at a shallow depth.
Furthermore, perched groundwater was observed along or near the contact between
surficial soils and the underlying sandstone. Based on our experience with sites underlain
by similar earth materials (clays), GSI estimates that the onsite soils are more consistent
with HSG “D” soils which have very slow infiltration rates (< 0.5 inches per hour) when
thoroughly wet.
Limiting Conditions
Soil Type
As indicated above, soils underlying the site consist of interbedded clay, clayey sand, and
sands. Within 6 feet of existing surface grades, soils are predominantly sandy clays.
Sandy clay typically exhibit infiltration rates less than 0.5 inches per hour. With remedial
grading, the actual infiltrate would be expected to further reduce due to a general
densification of material/reduction in available pore space. It should be noted that not
densifing this material (i.e., no remedial grading) the potential for distress to any overlying
settlement-sensitive improvement would increase.
These soils are also expansive. Periodic wetting and drying of these soils would increase
the potential for distress to relatively rigid improvements, such as foundations.
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Depth to Perched Groundwater
GSI (2015) indicates the presence of ground water at depths on the order of about 12 feet
below existing surface grades, and potentially within 10 feet of the infiltration surface,
where groundwater appears to be perched on the contact between surficial paralic
deposits of sand and clay, overlying dense formational sandstone. Generally “wet” soil
conditions above this depth attest to the capillary rise of this perched water, or former
groundwater rise, and/or and water vapor above this depth.
Geologic Structure
The site is underlain with surficial deposits of Quaternary-age paralic deposits, overlying
Eocene-age sedimentary bedrock, belonging to the Santiago Formation, at a depth of
about 10 to 12 feet below surface grades. The “Quaternary-Eocene unconformity” is
omnipresent throughout the area, and can be seen in the nearby coastal bluffs, where
seepage along this contact (from the same perched water table) results in spring sapping,
and erosion of the bluff face. Infiltration of storm water into onsite subsoils will have the
potential to contribute to this perched water table and the ultimate migration of subsurface
water toward the coastal bluff.
Utility Trenches
Utility trenches excavated into the clayey compacted fill will tend to act as french drains
and draw any nearby water into the trench. These trenches are ultimately tied into the
municipal system. As such, there is a strong potential for onsite utility trenches to collect
water from any unlined onsite BMP and convey water offsite, potentially resulting in
adverse settlements, and/or seepage within offsite properties. Saturation of soils around
utilities will also increase the potential for degradation/corrosion of susceptible piping, and
should be avoided.
Foundation Systems
Foundation systems, both planned and existing, would be adversely affected when in close
proximity to any storm water BMP. Increases in the potential for distress due to: water
vapor transmission through floor slabs and foundations, swelling of expansive soils, or
settlement due to a loss of bearing strength (soil saturation), would be realized.
Infiltration Feasibility
Based on the existing soil conditions, limiting factors discussed above, and the criteria
presented in BMP Manual Forms I-8, and I-9, onsite storm water BMPs should be designed
with respect to a “no infiltration” criteria, per the BMP manual.
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BMPs should use impermeable liners, and subdrains to direct subsurface water to a
suitable outlet/sump pump. Subdrains should consist of at least 3- to 4-inch diameter
Schedule 40 or SDR 35 drain pipe with perforations oriented down. The drain pipe should
be sleeved with a filter sock. Impermeable liners used should consist of a 30-mil polyvinyl
chloride (PVC) membrane, 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): 32 (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).
Plan Review
Our review of the City’s plan review document (City, 2018) provides comments related to
geotechnical/storm water issues in the “Land Development Engineering” section. For ease
of review, each comment (in italics) is reprinted below, with the appropriate response.
Land Development Engineering Comment No. 8
“Provide a soils report for the proposed project, including discussions and/or
recommendations for the following:
A:The pervious pavers are acceptable for infiltration and a lateral impermeable liner is
not require.
B.That private underground utilities are allowed under the driveway.
C.Buildings, both existing and proposed, are allowed adjacent to the pervious pavers.
D.Any Details for deepened footings, cut-off walls, etc.
E.Conclusions and recommendations.”
Response to Comment A:
Acknowledged. Pervious pavers are considered acceptable for storm water treatment.
However, based on the previous discussion of limiting factors, the pervious pavements
should be designed as a “flow through” system, per the BMP manual, and an impermeable
liner would be required.
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Response to Comment B:
Underground utilities would act as french drains per the discussion noted above, and
increase the potential for distress to both onsite and offsite improvements. Designing the
system as a “flow through” system would mitigate any adverse conditions. Alternatively,
any proposed utility backfill materials (i.e., inlet/outlet piping and/or other subsurface
utilities) located within or near the proposed area of the BMP 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 BMP, 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 BMP by geotextiles (liners) and/or slurry backfill.
Response to Comment C:
Both existing and planned structures/foundations would be adversely impacted by an
adjacent BMP system. Furthermore, a review of PLA (2018) indicates that the subgrade
surface for the permeable pavers is sloped toward the existing foundation system for an
offsite structure located at the property line. Mitigation for the planned structure would
include: a concrete mix design with a water/cement ratio of 0.5, or less, the use of a
minimum 15-mil, Class A, vapor retarder, and a deepened footing, extending at least
12 inches below the bottom of the adjacent BMP.
The existing foundation system is problematic. Existing foundation depths are not known,
and any excavation adjacent to the foundation could result in an adverse loss of lateral soil
bearing, resulting in an increased potential for distress to the offsite property. The
installation of a concrete cutoff barrier, at least 12 inches in width, and extending at least
12 inches below the bottom of the footing (current depth unknown), would be
recommended.
Response to Comment D:
Footings for the new structure should extend at least 12 inches below the bottom of the
adjacent BMP.
Footings for the adjacent, offsite structure should be provided with a concrete cut off wall,
at least 12 inches in thickness and extending at least 12 inches below the bottom of the
adjacent BMP. Concrete used in cut off wall construction should have a minimum
water/cement ratio of 0.5, or less. Cut off wall reinforcement per the structural engineer.
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Response to Comment E:
Conclusions and recommendations presented in this report are considered valid and
applicable.
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
2016 CBC. Consideration should be given to avoiding construction of planters adjacent
to structures. Site 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 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 due to their low plasticity
and granular nature. Consideration should be given to providing hay bales, straw waddles,
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 proposed
structures 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 structures, the sides and bottom of the
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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. Graded slope
areas should be planted with drought resistant vegetation. 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
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.
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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
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.
Recommendations for temporary slope construction are provided in a previous section of
this report. 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 interested/affected
parties, etc., that may perform such work.
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Utility Trench Backfill
1.All underground 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 (ASTM D 1557). 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,
provided this method is acceptable to the controlling agency. 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.
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/recertification.
•During shoring installation and 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, pavement, 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.).
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•During retaining wall subdrain installation, prior to backfill placement.
•During placement of backfill for area drain, interior plumbing, underground utility
line trenches, and retaining wall backfill.
•During slope construction/repair.
•When any unusual soil conditions are encountered during any construction
operations, subsequent to the issuance of this report.
•When any owner 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
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.
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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.
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.
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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.
Robert G. Crisman David W. Skelly
Engineering Geologist, CEG 1934 Civil Engineer, RCE 47857
RGC/DWS/JPF/jh
Attachments:Appendix A - References
Appendix B - Forms I-8 and I-9
Appendix C - General Earthwork, Grading Guidelines, and Preliminary
Criteria
Distribution:(2) Addressee
GeoSoils, Inc.
APPENDIX A
REFERENCES
GeoSoils, Inc.
APPENDIX A
REFERENCES
American Concrete Institute, 2014a, Building code requirements for structural concrete
(ACI 318-14), and commentary (ACI 318R-14): reported by ACI Committee 318,
dated September.
_____, 2014b, Building code requirements for concrete thin shells (ACI 318.2-14), and
commentary (ACI 318.2R-14), dated September.
_____, 2004, Guide for concrete floor and slab construction: reported by ACI Committee
302; Designation ACI 302.1R-04, dated March 23.
American Society for Testing and Materials (ASTM), 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, 2014, Supplement No. 2, Minimum design loads for
buildings and other structures, ASCE Standard ASCE/SEI 7-10, dated
September 18.
_____, 2013a, Expanded seismic commentary, minimum design loads for buildings and
other structures, ASCE Standard ASCE/SEI 7-10 (included in third printing).
_____, 2013b, Errata No. 2, minimum design loads for buildings and other structures,
ASCE Standard ASCE/SEI 7-10, dated March 31.
_____, 2013c, Supplement No. 1, minimum design loads for buildings and other structures,
ASCE Standard ASCE/SEI 7-10, dated March 31.
Blake, Thomas F., 2000, EQFAULT, A computer program for the estimation of peak
horizontal acceleration from 3-D fault sources; Windows 95/98 version.
Building News, 1995, CAL-OSHA, State of California, Construction Safety Orders, Title 8,
Chapter 4, Subchapter 4, amended October 1.
California Building Standards Commission, 2016a, California Building Code, California
Code of Regulations, Title 24, Part 2, Volume 2 of 2, based on the 2015 International
Building Code, 2016 California Historical Building code, Title 24, Part 8, 2016
California Existing Building Code, Title 24, Part 10, and the 2015 International
Existing Building Code.
GeoSoils, Inc.KB Home, Coastal, Inc.Appendix A
File:e:\wp9\7200\7203a.gua Page 2
_____, 2016b, California Building Code, California Code of Regulations, Title 24, Part 2,
Volume 1 of 2, Based on the 2015 International Building Code.
_____, 2016c, California green building standard code of regulations, Title 24, Part 11,
ISBN 978-1-60983-462-3.
Cao, T., Bryant, W.A., Rowshandel, B., Branum, D., and Willis, C.J., 2003, The revised 2002
California probalistic seismic hazard maps, dated June,
http://www.conversation.ca.gov/cgs/rghm/psha/fault_parameters/pdf/documents
/2002_ca_hazardmaps.pdf.
Carlsbad, City of, 2018, 1 Review for CT 2018-0004/RP 2018-0005 (DEV2017-0236) - Thest
Seaglass, Community and Economic Development, Planning Division, dated
March 22.
GeoSoils, Inc., 2015, Geotechnical evaluation, ‘The Wave,’ 2646 State Street, Carlsbad,
San Diego County, California, W.O. 6935-A-SC, dated November 3.
Kanare, H.M., 2005, Concrete floors and moisture, Engineering Bulletin 119, Portland
Cement Association.
Public Works Standards, Inc., 2012, “Greenbook,” standard specifications for public works
construction, BNi Building News, BNI Publications, Inc.
Post-Tensioning Institute, 2014, Errata to standard requirements for design and analysis
of shallow post-tensioned concrete foundations on expansive soils, PTI DC10.5-12,
dated April 16.
_____, 2013, Errata to standard requirements for design and analysis of shallow
post-tensioned concrete foundations on expansive soils, PTI DC10.5-12, dated
November 12.
_____, 2012, Standard requirements for design and analysis of shallow post-tensioned
concrete foundations on expansive soils, PTI DC10.5-12, dated December.
Safdie Rabines Architects, 2018, (Architectural plans For): The Seaglass, 2646 state Street,
Carlsbad, Ca. 92008, SRA Project No. 1713, dated February 22, 2018, by Safdie
Rabines Architects.
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, 2018, Civil Code, Sections 895 et seq.
GeoSoils, Inc.KB Home, Coastal, Inc.Appendix A
File:e:\wp9\7200\7203a.gua Page 3
U.S. Geological Survey, 2013, U.S. Seismic Design Maps, Earthquake Hazards Program,
http://geohazards.usgs.gov/designmaps/us/application.php, updated
June 23, 2014.
GeoSoils, Inc.
APPENDIX B
FORMS I-8 AND I-9
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:
The United States Department of Agriculture (USDA) has evaluated the infiltration rate of natural surface
soils as on the order of 0.57 to 1.98 in/hr (Hydrologic Soil Group B), based on soil taxonomy, which
characterized site soil as belonging to the “Marina Loamy Coarse Sand.” However, the USDA’s description
of the Marina Sand indicates that it is developed within eolian sand derived from mixed sources. Based
on our site exploration and review of regional geologic mapping, site soils are mapped as marine and
terrestrial “paralic” deposits derived from many regional formations, and typically contain local areas of fine
grained clay soils, such as noted on this site. Our experience with similar site soils in the vicinity, including
the geologic units observed and/or encountered during our subsurface investigation (GSI, 2015), indicate
that, in addition to the clayey nature of the soil, these soils typically become denser, and less permeable
with depth, below more permeable surficial layers of topsoil and colluvium. As such, the resultant
infiltration rates for these much denser formational materials would be expected to be well below the rate
evaluated by the USDA. Furthermore, artificial fill created by the recommended removal/recompaction of
onsite soils would also be considered to be of a very low permeability.
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:
No. The reduced permeability of recompacted surficial soils and formation at depth 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, etc., due to either soil saturation and settlement, or increased water
vapor transmission through slabs/foundations, with resultant distress. There is an increased potential for
the creation of perched groundwater (mounding) conditions along zones of contrasting permeabilities,
including shallow cut/fill contacts, transitions between potentially clayey and sandy formational materials
within the formation, and lateral migration of water toward nearby coastal bluffs, potentially contributing to
bluff erosion. Utility trenches can potentially act as french drains and provide conduits for the movement
of excessive moisture beneath the structure(s). Further such utility trenches would be subject to piping
and/or settlement in distress to overlying improvements, both onsite and offsite.
Summarize findings of studies; provide reference to studies, calculations, maps, data sources, etc. Provide narrative discussion
of study/data source applicability.
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:
No. While this study did not include an environmental assessment, visual observation did not indicate the
presence of potential contaminants. 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:
Yes. The site currently drains offsite into the regional storm water system and no significant runoff appears
to be retained onsite. An infiltration BMP would reduce runoff into the adjacent lagoon. The groundwater
table is 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
No
* 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.
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:
The United States Department of Agriculture (USDA) has evaluated the infiltration rate of natural surface soils
as on the order of 0.57 to 1.98 in/hr (Hydrologic Soil Group B), based on soil taxonomy, which characterized site
soil as belonging to the “Marina Loamy Coarse Sand.” However, the USDA’s description of the Marina Sand
indicates that it is developed within eolian sand derived from mixed sources. Based on our site exploration and
review of regional geologic mapping, site soils are mapped as marine and terrestrial “paralic” deposits derived
from many regional formations, and typically contain local areas of fine grained clay soils, such as noted on this
site. Our experience with similar site soils in the vicinity, including the geologic units observed and/or
encountered during our subsurface investigation (GSI, 2015), indicate that, in addition to the clayey nature of
the soil, these soils typically become denser, and less permeable with depth, below more permeable surficial
layers of topsoil and colluvium. As such, the resultant infiltration rates for these much denser formational
materials would be expected to be well below the rate evaluated by the USDA. Furthermore, artificial fill created
by the recommended removal/recompaction of onsite soils would also be considered to be of a very low
permeability.
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 reduced permeability of compacted clay fill near the surface and dense formation at depth 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, etc., due to either soil saturation and settlement, or increased water vapor
transmission through slabs/foundations, with resultant distress. There is an increased potential for the creation
of perched groundwater (mounding) conditions along zones of contrasting permeabilities, including shallow
cut/fill contacts, and transitions between potentially clayey and sandy formational materials within the formation.
Lateral migration of perched water in this area is also known to maanifest as seepage from the nearby coastal
bluffs. Utility trenches can potentially act as french drains and provide conduits for the movement of excessive
moisture beneath the structure(s). Further such utility trenches would be subject to piping and/or settlement
resulting in distress to overlying improvements, both onsite and offsite.
Summarize findings of studies; provide reference to studies, calculations, maps, data sources, etc. Provide narrative
discussion of study/data source applicability.
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:
No. 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.
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:
Water rights are considered a legal matter, and typically do not fall within the purview of geotechnical
engineering. GSI is not aware of any downstream water rights issues of concern on the adjoining
properties. Further, given the low infiltration rate of onsite soils, it does not appear that infiltration should
significantly affect downstream water frights, from a geotechnical perspective. Further, drainage appears
to be directed offsite into the regional storm water system. The depth to groundwater is about 10 feet, or
less, below the bottom of the anticipated BMP elevation.
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.
Appendix D: Approved Infiltration Rate Assessment Methods
D-19 February 26, 2016
Form I-9: Factor of Safety and Design Infiltration Rate Worksheet, Seaglass W.O. 7452-A-SC
Factor of Safety Infiltration Rate Worksheet FORM I-9
Factor Criteria Factor Description Assigned
Weight (w)
Factor
Value (v)
Product (p)
p = w x v
A Suitability
Assessment
Soil assessment methods 0.25 3 0.75
Predominant soil texture 0.25 1 0.25
Site soil variability 0.25 2 050
Depth to groundwater/impervious layer 0.25 2 0.50
ASuitability Assessment Safety Factor, S = Ep 1.75 Use 2.0
B Design
Level of pretreatment/expected sediment loads 0.5
Redundancy/resiliency 0.25
Compaction during construction 0.25
BDesign Safety Factor, S = Ep
total A BCombined Safety Factor, S = S x S
observedObserved Infiltration Rate, inch/hr, K
(corrected for test-specific bias)
design observed totalDesign Infiltration Rate, in/hr, K = K / S
Supporting Data
Briefly describe infiltration test and provide reference to test forms:
GeoSoils, Inc.
APPENDIX C
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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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
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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 Code, 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
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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
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as a plane up from the lower-most heel of the retaining structure, to the daylight grade of
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
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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
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.
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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
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
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representative (supervisor, grade checker, dump man, operator, etc.) should direct
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.