HomeMy WebLinkAbout; La Costa Meadows Unit 3; Preliminary Soils Report; 1997-04-01PRELIMINARY GEOTECHNICAI, INVESTIGATION,
LOTS 5 18 THROUGH 52 1 AND LOT 523 OF
LA COSTA MEADOWS UNIT 3,
CARLSBAD. CALIFORNIA
April 1, 1997
Project No. 4971053-001
Prepared For:
TRC DEVELOPMENT CORPORATION
27381 Celanova
Mission Viejo, California 92692
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3934 MURPHY CANYON ROAD, SUITE 8205. SAN DIEGO, CA 92 I23
(619) 292-8030 * (800) 447-2626
FAX (6 19) 292-077 I
April 1, 1997
Project No. 4971053-001
To: TRC Development Corporation
27381 Celanova
Mission Viejo, California 92692
Attention: Mr. Scott Redsun
Subject: Preliminary Geotechnical Investigation, Lots 518 through 521 and Lot 523 of La Costa
Meadows Unit 3, Carlsbad, California
In accordance with your request, we have performed a preliminary geotechnical investigation of Lots 5 18
through 521 and Lot 523 of La Costa Meadows, located in Carlsbad, California. Based on the results of
our investigation, the site was previously sheet-graded with observation and testing services performed by
others (Benton, 1972). The purpose of our investigation was to evaluate the existing site geotechnical
conditions and review the available geotechnical and geologic reports and maps pertinent to the site. This
report presents our findings, conclusions and recommendations regarding the existing condition of the
subject site and the proposed improvements.
Based on the results of our investigation, review of the reports pertinent to the site and knowledge of the
planned improvements, the proposed development is considered feasible from a geotechnical standpoint,
provided the recommendations outlined in this report are implemented during grading and construction.
If you have any questions regarding our report, please. contact this ofice. We appreciate this opportunity
to be of service.
Respectfully submitted,
L,EI,$37TON AND ASSOCIATES. INC.
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Distribution: (6) Address# - I$" No. - ""
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3934 MURPHY CANYON ROAD, SUITE B205, SAN DIEGO, CA 921 23
(6 19) 292-8030 - (800) 447-2626
FAX (6 19) 292-077 I
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TABLE OF CONTENTS .
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Section &
1.0 INTRODUCTION ..................................................... 1
1.1 Purpose and Scope of Services ......................................... 1
1.2 Site and Project Description ........................................... 3
1.3 Subsurface Investigation and Laboratory Testing ............................ 3
2.0 GEOTECHNICAL CONDITIONS .......................................... 6
2.1 Regional Geology .................................................. 6
2.2 Site-Specific Geology ............................................... 6
2.2.1 Artificial Fill - Existing (Map Symbol - Afo) .......................... 6
2.2.2 Torrey Sandstone (Map Symbol - Tt) ............................... 6
2.2.3 Del Mar Formation (Map Symbol - Td) .............................. 7
2.4 Landslides and Surficial Slope Failure 7
2.3 Geologic Structure 7
2.5 Faulting ........................................................ 7
2.6 Seismicity ....................................................... 8
2.6.1 Ground Shaking .............................................. 8
2.6.2 Ground Rupture .............................................. 8
2.6.3 Liquefaction and Dynamic Settlement ............................... 8
2.7 Groundwater .................................................... 9
3.0 EVALUATION OF EXISTING FILL SOILS AND GEOTECHNICAL CONDITIONS ..... 10
................................................. ....................................
3.1 Laboratory Testing ................................................ 10
3.2 Cut/Fill Transition Lots ............................................. 10
4.0 CONCLUSIONS ..................................................... 11
5.0 RECOMMENDATIONS ................................................ 13
5.1 SiteEarthwork ................................................... 13
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TABLE OF CONTENTS (continued)
5.1.1 Site Preparation ............................................. 13
5.1.3 Stability Fill for Slope on East Side of Lot 523 ....................... 14
5.1.6 Trench Backfill and Compaction .................................. 15
5.1.7 Grading of Expansive Soils ..................................... 15
5.1.2 Removal and Recompaction ..................................... 13
5.1.5 Overexcavation of Cut/Fill Transition Conditions 15
5.1.4 Fill Placement and Compaction 14 ................................... ......................
5.2 Post-Tensioned Foundation Design Considerations .......................... 15
5.2.2 Foundation Setback from Slope Face 18
5.2.1 Moisture Conditioning 17 ......................................... ...............................
5.3 Lateral Earth Pressures and Retaining Wall Design Considerations ............... 19
5.4 Cement Type for Construction ........................................ 22
5.5 Private Concrete Driveways .......................................... 22
5.6 Graded Slopes ................................................... 22
5.7 Control of Surface Water and Drainage Control ............................ 22
5.9 Construction Observation and Testing 23
5.8 Preliminary Pavement Design 22 ........................................ ...................................
Fieures
Figure 1 - Site Location Map ................................................ 2
Figure 3 - Retaining Wall Drainage Detail ....................................... 21
Figure2-GeotechnicalMap .................................................. 5
Tables
Table 1 - Post-Tensioned Foundation Design Recommendations ......................... 16
Table 2 - Minimum Presaturation Recommendations for Post-Tensioned Foundation Subgrade Soils 17
Table 3 - Minimum Foundation Setback from Slope Faces ............................ 18
Table 4 - Lateral Earth Pressures .............................................. 19
Amendices
Appendix A - References
Appendix B - Boring Logs
Appendix C - Laboratory Test Results and Test Procedures
Appendix D - General Earthwork and Grading Specifications for Rough Grading
1.0 INTRODUCTION
1.1 Pumose and Scow of Services
This report has been prepared in accordance with your request and presents the results of our
geotechnical investigation for Lots 518 through 521 and Lot 523 of La Costa Meadows Unit 3,
Carlsbad, California (see Site Location Map, Figure 1). The purpose of our preliminary investigation
was to evaluate the pertinent geotechnical conditions at the site and to provided preliminary design
criteria relative to the proposed development of the site. Our scope of services included:
Review of pertinent available literature (including previous geotechnical reports), geologic maps,
and aerial photographs (Appendix A). . Site reconnaissance and geologic mapping.
A subsurface exploration consisting of the excavation, sampling and logging of six large
diameter exploratory borings. The borings were excavated to evaluate the engineering
characteristics of the existing fill soils which were previously placed by others and the
characteristics of the adjacent and underlying formational materials. Logs of the borings are
presented in Appendix B.
Laboratory testing of representative samples obtained during our subsurface investigation
(Appendix C).
Geotechnical analysis of the data obtained.
Preparation of this report presenting our findings, conclusions and recommendations with respect
to the proposed site development.
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TRC - Carlsbad Project No. SITE Lots 518-521 and 523
Carlsbad, California MAP
LOCATION
4971053-001
La Costa Meadows Unit 3 Date 1042 889 4-1 -97 Figure No. 1
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1.2 Site and Proiect Descriotion
The subject site is located northwest of the intersection between Unicornio and El Fuerte Streets in
the City of Carlsbad, California (Figure 1). The property consists of two separate parcels which
include Lots 5 18 through 521 and Lot 523 of the La Costa Meadows Unit 3 Subdivision. The site
is bounded by residential structures to the north and west, by Unicornio Street to the south and by
El Fuerte Street to the east. Lot 522, located in the middle of the two parcels comprising the site,
is not a part of the project.
The site was rough-grading in 1972 (Benton, 1972). Grading of the site included the construction
of relatively level building pads, small (less than 5-foot high) side-yard slopes between the lots, a
5- to 25-foot tall east-facing slope on the east side of Lot 523, and an approximately 60-foot tall
north-facing slope along the north side of the lots. All the slopes on the site are fill slopes with
approximate slope inclinations of 1.5 to 1 (horizontal to vertical) or flatter. The large north-facing
fill slope has an approximately 10 to 20 foot wide flat bench at mid-height in the slope.
Based on our subsurface investigation and review of a compacted fill report in the City of Carlsbad
files, the site has a cut/fill transition condition crossing through a portion of Lots 518 through 521.
Fill soils up to approximately 10 to 15 feet thick are present in the northwestern portion of the site,
while fill soils up to approximately 50+ feet are located on the east side (i.e. Lot 523). Existing on-
site improvements include a storm drain system in the easement between Lots 519 and 520 and
underground utilities along the south and east sides of the property.
The proposed development will consist of 21 single-family residential structures, associated
improvements and anticipated paved common driveways. The development will consist of the
construction of four complexes of 4 to 6 residential structures around a "court-yard" common
driveway. We anticipate that grading of the site will include the recornpaction of potentially
compressible and desiccated fill soils and weathered formational material, the overexcavation of the
building pads having cut/fill transition conditions, the placement of fill, the excavation of cut, and
the construction of building pads and associated driveways. We anticipate that post-grading will
include the installation of underground utilities and the placement of a pavement section in the
driveways.
1.3 Subsurface Investigation and Laboratory Testing
Our subsurface investigation consisted of the excavation of six largediameter borings. The borings
were excavated to a maximum depth of 59 feet utilizing a 30-inch diameter bucket drill rig. The
borings were excavated to evaluate the engineering characteristics of the existing fill soils and
formational material. All borings were logged by our geologist who obtained representative bulk
and undisturbed samples of the soils encountered for laboratory testing. The larger diameter borings
were also entered by our geologist and downhole logged. Logs of all of the borings are presented
in Appendix B. Boring locations are shown on the Geotechnical Map (Figure 2). Subsequent to the
subsurface investigation, the excavations were backfilled and tamped. Some settlement of the
backfill soils should be expected with time.
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Laboratory testing was performed on representative soil samples and included moistuddensity
determination, expansion potential and hydrocollapse potential tests. A discussion of the tests
performed and a summary of the results are presented in Appendix C. The densityhoisture
determinations of the undisturbed samples obtained from the borings are shown on the boring logs
(Appendix B).
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2.0 GEOTECHNICAL CONDITIONS
2.1 Regional Geology
The project is situated in the coastal section of the California Peninsular Range, a geomorphic
province within a long and active geologic history. This region is more specifically known as the San
Diego Embayment, an area which has undergone several episodes of marine inundation and
regression during the last 54 million years. This has left a thick sequence of marine and nonmarine
sediments overlying the Southern California batholith. Recent topographic uplifts has lead to the
erosion of these creating the canyon and ridgelines seen today.
2.2 Site-Specific Geology
Based on our subsurface exploration and review of pertinent geologic and geotechnical literature
(Appendix A), the area of the proposed development is located on the western side of an in-filled
northwest trending canyon. Existing fill soils are present in the northwest, north and east sides of
the property. Silty sandstones of the Torrey Sandstone are exposed in the southwest portion of the
site beneath a thin veneer of fill material. The Torrey Sandstone was also encountered at depth
beneath artificial fill,. with the depth to bedrock increasing to the northeast and east. A buried
depositional contact exists in the northeast corner of the site between the Torrey Sandstone and
underlying Del Mar Formation. It should be noted that both the Torrey Sandstone and fill soils at
present grade have become weathered and will require reprocessing as specified in Section 5.1.2.
A brief description of each of the units is provided below.
2.2.1 Artificial Fill - Existing (Map Symbol - Afo)
As encountered in our borings, the fill soils encountered ranged in thickness from a thin
veneer (approximately 0.5 feet thick encountered in Borings LB-3 and LB-4) to 49 feet as
encountered in Boring LB-2. As depicted on Figure 2, Boring LB-3 is located at the
southwest corner of the site and Boring LB-2 is located at the northwest corner of the site
in the area of maximum fill depth. These fill materials, derived from the underlying Torrey
Sandstone and Del Mar Formation, consisted of light gray to brown, moist, medium dense
silty fine to medium sand and sandy clay with occasional pebbles. The fill soils are
anticipated to possess a low to high expansion potential, a relatively high in-place density
and good bearing characteristics.
2.2.2 Torrev Sandstone Nap Symbol - Tt)
The Tertiary-aged Torrey Sandstone underlies all but the northeast portion of the site. This
unit is exposed along the southern approximate third of the site partially covered by a thin
veneer of fill. As encountered, this material consisted of pale gray to light brown, damp
to moist, dense to very dense, silty sand with isolated areas of iron-oxide stained bedding.
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This material typically has good bearing characteristics and a very low to low expansion
potential.
2.2.3 Del Mar Formation (Map Symbol - Td)
The Tertiary-aged Del Mar Formation was encountered in Boring LB-2 in the northeast
corner of the site at a depth of 49 feet below the existing finish grade elevation on Lot 523.
As encountered during our field investigation, this unit consisted of light gray-green, damp,
very dense, silty fine sandy claystone, moderately fractured and sheared. These soils have
a high to very high expansion potential. With the exception of the clayey fill soils derived
from the Del Mar Formation, we do not anticipate that these formational materials will be
encountered during site grading or development.
2.3 Geoloeic Structure
Based on our subsurface investigation, site reconnaissancdgeologic mapping, literature review and
our professional experience on nearby sites, bedding on site is flat lying to slightly dipping to the
west.
2.4 Landslides and Surficial Sloae Failure
Based on our subsurface investigation, site reconnaissancdgeologic mapping and review of the
geologic literature pertinent to the site, there is no indication of landslides within the proposed
development area. However, a shallow landslide or surficial failure was identified in the east-facing
fill slope along El Fuerte Street (at the northeast corner of Lot 523). The area of failure is
characterized by hummocky and irregular topography, a steep head-scarp near the top of the existing
fill slope, and loose soil piled against existing tree trunks adjacent to the curb on the west side of
El Fuerte Street. Although this surficial failure does not appear to threaten the structural integrity
of Lot 523 at this time, we recommend that the surficial failure be removed to competent material,
a stability fill constructed, and the slope face regraded during site development. Geotechnical
recommendations concerning the repair of the surficial slope failure are presented in Section 5.1.3.
2.5 Faulting
Our discussion of faults on the site is prefaced with a discussion of California legislation and state
policies concerning the classification and land-use criteria associated with faults. By definition of
the California Mining and Geology Board, an & fault is a fault which has had surface
displacement within Holocene time (about the last 11,000 years). The State Geologist has defined
a potentiallv active fault as any fault considered to have been active during Quaternary time (last
1,600,000 years). This definition is used in delineating Fault-Rupture Hazard Zones as mandated
by the Alquist-Priolo Earthquake Fault Zoning Act of 1972 and as most recently revised in 1994.
The intent of this act is to "regulate development near active faults so as to mitigate the hazard of
surface fault rupture" (Hart, 1994). Based on our review of the Fault-Rupture Hazard Zones, the site
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is not located within any Fault-Rupture Hazard Zone as created by the Alquist-Priolo Act (Hart,
1994).
No active faults are known to exist in the immediate vicinity of the site and none were encountered
in the course of our investigation or previous investigations. The nearest known active fault is the
Rose Canyon Fault Zone, located approximately 8 miles west of the site.
2.6 Seismicie
The subject property can be considered to lie within a seismically active region, as can all of
southern California. Seismic hazards that may affect the site include ground shaking, ground rupture
along a pre-existing fault, liquefaction and dynamic settlement. The seismic hazards affecting the
site are discussed below:
2.6.1
2.6.2
2.6.3
Ground Shaking
The seismic hazard most likely to impact the site is ground shaking resulting from an
earthquake on one of the major regional active faults. Due to the relatively close proximity
of the Rose Canyon Fault Zone to the site, the most significant ground shaking from one
of the regional faults will most likely occur on the Rose Canyon Fault Zone. A maximum
credible earthquake of moment magnitude 6.9 on the Rose Canyon Fault Zone could
produce a peak horizontal ground acceleration of 0.34g. Based on the Uniform Building
Code criteria, the site lies within Seismic Zone 4. For design purposes, however, an
effective ground acceleration of 0.40g based on Uniform Building Code (ICBO, 1994)
criteria, should be assumed.
Ground Ru~ture
Ground rupture generally is considered to occur along pre-existing fault strands. Since no
active faults have been mapped crossing the site or in the general vicinity of the site, ground
rupture is considered unlikely.
Liouefaction and Dvnamic Settlement
Liquefaction and dynamic settlement of soils can be caused by strong vibratory motion due
to earthquakes. Both research and historical data indicate that loose, saturated, granular
soils are susceptible to liquefaction and dynamic settlement while the stability of silty clays
and clays is not adversely affected by vibratory motion (Seed, 1982). Liquefaction is
typified by a total loss of shear strength in the affected soil layer, thereby causing the soil
to flow as a liquid. This effect may be manifested by excessive settlements and sand boils
at the ground surface.
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Due to the lack of a permanent ground water table within the proposed limits of grading
and the fine-grained and relatively stiff to hard nature of the onsite clayey soils, it is our
opinion that the liquefaction potential of these soils due to the design earthquake event is
considered low.
2.7 Ground Water
Ground water was not encountered during our subsurface investigation. Ground water is not
anticipated to be encountered, and accordingly, it not expected to be a significant constraint to site
development. However, our experience indicates that seepage conditions can be caused by irrigation
practices in areas where no seepage or ground water was observed prior to development. These
seepage conditions, if they occur, should be mitigated on a case by case basis.
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3.0 EVALUATION OF EXISTING FILL SOILS AND GEOTECHNICAL CONDITIONS
3.1 Laboratory Testinq
Laboratory testing of the existing fill soils was performed on representative samples obtained from
the borings and included the determination of the in-place moisture and density, expansion potential
and hydrocollapse potential. The results of our laboratory testing are presented on the boring logs
(where appropriate) and Appendix C.
The results of our testing indicate, that in general, the fill soils tested were moderately to well
compacted, moist, and should perform as anticipated. Degree of saturation calculations and
hydrocollapse testing indicated a low settlementheave potential upon future wetting. The near-
surface soils (upper 5 feet) possess a low to medium potential for expansion based on our
geotechnical observation and limited testing. However, soils of high expansion potential (expansion
index between 5 1 and 90) may exist on the site.
3.2 Cut/Fill Transition Lots
From the results of our subsurface investigation and our review of the preliminary site plan by
Dawson, Hannouche, Pate Architectural Planning (Dawson, 1997), a cut/fill transition will most
likely occur beneath some of the proposed structures on Lots 518 through 521. Based on the
preliminary site plan pawson, 1997), approximately 5 to 7 structures will be located across the
existing cut/fill transition. However, the actual structures affected by the transition will need to be
identified during site grading by the geotechnical consultant. Special grading procedures (i.e. the
overexcavation of the upper 3 feet of the cut portion of the pad and the replacement with compacted
fill) will be necessary for structures over cut/fill transitions. Geotechnical recommendations
concerning the cut/fill transition conditions are presented in Section 5.1.5.
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4.0 CONCLUSIONS
Based on the results of our preliminary geotechnical investigation and our review of the previous
geotechnical and geologic reports, it is our opinion that the proposed development of Lots 5 18 through
521 and Lot 523 of La Costa Meadows Unit 3 is feasible from a geotechnical standpoint, provided the
following conclusions and recommendations are incorporated into the project plans, specifications, and
followed during site grading and construction.
The following is a summary of the geotechnical factors which may affect future development of the site.
Based on our subsurface exploration and review of pertinent geotechnical reports, the site is
underlain by the existing fill soils, Torrey Sandstone, and the Delmar Formation.
The upper 1 to 2 feet of the existing fill and formational materials on the lots are desiccated, dry,
loose, and potentially compressible in their present state and will require removal and recompaction.
Due to the construction of the site in the early 1970's when slopes having 1.5:l (horizontal to
vertical) slope inclinations were commonly built, the side-yard slopes and east-facing slope on the
east side of Lot 523 are steeper than what the current City of Carlsbad Grading Ordinance allows.
As a result, the slope should either be regraded with a 2: 1 (horizontal to vertical) slope inclination
and/or a retaining wall constructed.
The surficial slope failure on the east-facing fill slope (at the northeast comer of Lot 523) should be
removed to competent soil and replaced with a stability fill. Geotechnical recommendations are
presented in Section 5.1.3.
It is anticipated that the on-site soils may be excavated with conventional heavy-duty construction
equipment. Localized cemented zones may required heavy ripping.
The existing on-site soils appear to be suitable material for use as fill provided they are relatively
free of rocks (larger than 6 inches in maximum dimension), organic material and debris.
Active faults are not known to exist on or in the immediate vicinity of the site.
The main seismic hazard that may af€ect the site is from ground shaking from one of the active
regional faults.
The maximum anticipated bedrock acceleration on the site due to a earthquake on the Rose
Canyon Fault Zone of moment magnitude 6.9 is estimated to be 0.34g with an effective ground
acceleration of approximately 0.40g (ICBO, 1994).
Due to the clayey and/or relatively dense nature of the on-site soils, the potential for liquefaction and
dynamic settlement of the site is considered unlikely, providing the recommendations for site grading
(as indicated in Section 5.1 and Appendix D) are. adhered to.
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Ground water or seepage conditions were not observed on the site during our investigation.
Therefore, ground water on the site is not anticipated to be a significant factor during site grading
and subsequent development. If ground water seepage conditions are encountered during site
development, recommendations to mitigate the conditions can be made on a case-by-case basis.
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5.0 RECOMMENDATIONS
5.1 Site Earthwork
We anticipate that earthwork at the site will consist of site preparation, removals of potentially
compressible soil, excavation of cut material, fill placement, and trench excavation and backfill. All
fill slopes (with the exception of the north-facing fill slope on the north side of the lots) should be
regraded so the slope has a maximum 2: 1 (horizontal to vertical) slope inclination andor constructed
with a retaining wall (see Section 5.3).
We recommend that earthwork on-site be performed in accordance with the following
recommendations, the City of Carlsbad grading requirements, and the General Earthwork and
Grading Specifications for Rough Grading (GEGS) included in Appendix D. In case of conflict, the
following recommendations shall supersede those included as part of Appendix D.
5.1.1
5.1.2
Site Preoaration
Prior to grading, the site should be cleared of debris and stripped of vegetation. Vegetation
and debris should be disposed off-site. Holes resulting from removal of buried obstructions
which extend below finished site grades should be filled with properly compacted soil.
Removal and RecomDaction
The upper mne of fill and formational soils that occur on site are relatively dry, desiccated,
loose, and potentially compressible in their present state and may settle under the surcharge
of fills or foundation loadings. In areas that will receive additional fill soils andor support
settlement-sensitive structures or other improvements (such as driveways, hardscape,
retaining walls, etc.), these soils should be removed to a depth of 1 to 2 feet below existing
grade, moisture-conditioned (as needed to obtain a near optimum moisture content), and
recompacted to a minimum of 90 percent relative compaction (based on American Standard
of Testing and Materials [ASTM] Test Method D1557-91) prior to placing additional fill.
In the areas of the proposed structures, removals should extend a minimum of 2 feet below
existing ground surface, have all rocks greater than 6 inches in maximum dimension and
construction debris removed, moisture conditioned and recompacted to a minimum 90
percent relative compaction (per ASTM Test Method D1557-91). Removals should be
accomplished to a minimum of 5 feet (measured laterally) beyond building, pavement and
hardscape perimeters. Depths and limits of removals should be evaluated by the
geotechnical consultant during site grading prior to fill placement and may locally vary from
what is presented herein. The required depth should be evaluated by the geotechnical
consultant during site preparation.
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5.1.3 Stabilitv Fill for Slope on East Side of Lot 523
Based on the site reconnaissance of the property, a surficial slope failure was identified in
the east-facing fill slope at the northeast comer of Lot 523. As observed, the surficial slope
failure appears to be 4 to 6+ feet thick, approximately 100-feet long and extends almost to
the top of the existing slope. A 1- to 2-foot high back scarp near the top of the slope and
loose piled soil adjacent to the curb are also apparent.
We recommend that the surficial slope failure be completely removed to competent fill
material and the slope replaced with a stability fill. Since the slope is currently graded at
a slope inclination of 1.5 to 1 (horizontal to vertical) which is steeper than currently
allowed, we recommend that the slope also be regraded to a 2:1 slope inclination. Since
flattening the slope will also increase the area of the slope (and consequently reduce the size
of the building pad of Lot 523), a retaining wall at the toe-of-slope may be considered to
keep the top-of-the-slope at the same location. An alternative would be to reconstruct the
slope at a 1.5 slope inclination utilizing geogrid slope reinforcement. Specific geotechnical
recommendations concerning the use of geogrid slope reinforcement can be provided under
separate cover.
The stability fill should have a minimum width of IO-feet and extend all the way up to the
top of slope. The stability fill key should be constructed a minimum of 2 feet below the
curb subgrade elevation and the key bottom angled at least 2 percent into-the-slope. The
stability fill backcut should not be steeper than a 1:1 slope inclination. A subdrain system
consisting of 4-inch diameter perforated pipe surrounded by a minimum of 3 cubic feet (per
linear foot) of crushed 3/4-inch gravel and wrapped in filter fabric (Mirafi 140N or
equivalent) should be placed along the bottom of the backcut and outletted through the curb
face (on the downhill side of the stability fill). Construction of the stability fill should be
scheduled so that the amount of time the backcut is open is kept to a minimum (10 days
maximum). If the stability fill is constructed during the rainy season and if precipitation
is forecasted, visqueen sheeting should be placed on the backcut to reduce the potential for
erosion and additional surficial slope failures. A typical detail of the recommended stability
fill and subdrain is presented in Appendix D.
5.1.4 Fill Placement and Comwction
The on-site soils are generally suitable for use as compacted fill, provided they are screened
of rock greater than 6 inches in dimension, organic materials and construction debris. Areas
prepared to receive structural fill and/or other surface improvements should be scarified to
a minimum depth of 6 inches, brought to at least optimum moisture content, and
recompacted to at least 90 percent relative compaction (based on ASTM Test Method
01557-91). The optimum lift thickness to produce a uniformly compacted fill will depend
on the type and size of compaction equipment used. In general, fill should be placed in
uniform lifts not exceeding 8 inches in compacted thickness. Fill soils should be placed at
a minimum of 90 percent relative compaction (based on ASTM Test Method D1557-91) at
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or above optimum moisture content. In the common driveways, soils should be compacted
to 95 percent relative compaction within 1 foot of finished grade. Placement and
compaction of fill should be performed in accordance with local grading ordinances under
the observation and testing of the geotechnical consultant.
Import soils, if necessary, should consist of granular soils of very low to low expansion
potential (expansion index 50 or less based on UBC 18-2) and contain no materials over 6
inches in maximum dimension.
5.1.5 Overexcavation of Cut/Fill Transition Conditions
For structures in cut/fill transition areas, preparation shall consist of undercutting the soils
in the cut portion of the pad. Undercutting will entail a 3-fOOt removal and recompaction.
This 3 foot depth shall be measured down from planned slab subgrade elevation. The
undercut shall extend a minimum of 5 feet laterally outside the building perimeter.
Recompacted soil shall be properly moisture conditioned (as needed) and recompacted to
at least 90 percent relative compaction (based on ASTM Test Method D1557-91).
5.1.6 Trench Backfill and Comoaction
The on-site soils may generally be suitable as trench backfill provided they are screened
rocks and other material over 6 inches in diameter and organic matter. Trench backfill
should be compacted in uniform lifts (not exceeding 8 inches in comoacted thickness) bv
mechanical m&s to at least 90 percent relative compaction (per ASTM Test Method
D1557-91).
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5.1.7 Grading of Exoansive Soils
Moderately to highly expansive soil may be present within the upper 5 feet of the existing
pad grade elevations. If expansive soils are utilized at pad grade, typical expansive soil-
related distress (such as cracked flatwork and stucco, poor vegetation growth, etc.) may be
expected over the life of the project. Accordingly, we recommend that expansive soils
(encountered during grading operations as identified by the geotechnical consultant) be
placed 2 to 3 percent above optimum moisture content (and greater if possible) and a heavy
reinforcement schedule be used for the proposed improvements. Geotechnical
recommendations concerning the proposed residential structures which may be constructed
on expansive soils is presented in Section 5.2.
5.2 Post-Tensioned Foundation Desien Considerations
We understand the proposed buildings will be one- to two-story, of wood-frame construction and
utilize a post-tensioned slab-on-grade floor system. Foundations and slabs should be designed by
a structural engineer in accordance with structural considerations and the following recommendations.
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4971053-001
These recommendations assume that the soils in the upper 3 feet of finish grade will have a low to
high potential for expansion (an expansion index between 20 and 120 per UBC 18-I-B). The actual
expansion potential of the finish grade soils of the building pads should be evaluated upon
completion of the fine-grading operations so that final geotechnical design recommendations can be
made on a lot by lot basis.
We recommend slabs be designed in accordance with the following design parameters, based on
criteria of the Post-Tensioning Institute.
Table 1
Post-Tensioned Foundation Design Recommendations
Expansion Index (VBC 18-I-B)
Design Criteria High Medium LOW
(0 - 50) (91-130) (51 - 90)
Edge Moisture
0.52 inches 0.25 inches 0.25 inches Edge Lift: Swell, y,
4.1 inches 2.42 inches 0.60 inches Center Lift: Differential
2.5 feet 2.5 feet 2.5 feet Edge Lift: Variation, e,
5.5 feet 5.5 feet 5.5 feet Center Lift:
I I Anticipated Settlement: Total Settlement = 3/4 inches
Differential Settlement = 1/2 inches II
Allowable Bearing Capacity: 2,000 psf 2,000 psf 2,000 psf
The expansion potential for each lot should be provided at the completion of the fine grading when
actual pad grade soils can be tested. The allowable bearing capacity may be increased by onethird
for short-term wind or seismic loads. Exact foundation design can be provided by a qualified
structural engineer, based on the above parameters.
Slabs should be underlain by a minimum of 2 inches of clean sand (sand equivalent >30) which is
in turn underlain by a vapor barrier. The vapor barrier should be sealed at all penetrations and laps.
We recommend that the vapor barrier be also underlain by a 2 inch layer of clean sand (sand
equivalent grater than 30) to act as a capillary break.
Moisture vapor transmission may be additionally reduced by use of concrete additives. Moisture
barriers can retard, but no eliminate moisture vapor movement from the underlying soils up through
the slabs. We recommend that the floor coverings installer test the moisture vapor flux rate prior
to attempting applications of the flooring. "Breathable" floor coverings should be considered if the
vapor flux rates are high. A slipsheet or equivalent should be utilized above the concrete slab if
crack-sensitive floor coverings (such as ceramic tiles, etc.) are to be placed directly on the concrete
slab.
- 16-
4971053-001
Our experience indicates that use of reinforcement in slabs and foundation will generally reduce the
potential for drying and shrinkage cracking. However, some cracking should be expected as the
concrete cures. Minor cracking is considered normal; however, it is often aggravated by a high
waterkement ratio, high concrete temperature at the time of placement, small nominal aggregate size,
and rapid moisture loss due to hot, dry and/or windy weather conditions during placement and
curing. Cracking due to temperature and moisture fluctuations can also be expected. The use of low
slump concrete (not exceeding 4 to 5 inches at the time of placement) can reduce the potential for
shrinkage cracking and the action of tensioning the tendons can close small shrinkage cracks. In
addition to the careful control of waterhment ratios and slump of concrete, application of 50 percent
of the design post-tensioning load within three to four days of slab pour is found to be an effective
method of reducing the cracking potential.
Presaturation of the slab subgrade soils underlying post-tensioned foundation systemsmay be omitted
provided the slab subgrade soils have a very low to low expansion potential (less than 50 per U.B.C.
18-I-B).
5.2.1 Moisture Conditioning
The slab subgrade soils underlying the post-tensioned foundation systems should be
presoaked in accordance with the recommendations presented in Table 2 prior to placement
of the moisture barrier and slab concrete. The subgrade soil moisture content should be
checked by a representative of Leighton and Associates prior to slab construction.
Table 2
Minimum Presaturation Recommendations for Post-Tensioned
Foundation Subgrade Soils
Expansion Potential
(UBC 18-EB) Presoaking Recommendations
Very Low to Low Near-optimum moisture content to a depth of 6
inches
Medium
content to a minimum depth of 18 inches
Minimum of 1.3 times the optimum moisture
below slab subgrade
High Minimum of 1.4 times the optimum moisture
content to a minimum depth of 24 inches
below slab subgrade
Presoaking or moisture conditioning may be achieved in a number of ways. But based on
our professional experience, we have found that minimizing the moisture loss on pads that
have been completed (by periodic wetting to keep the upper portion of the pad from drying
out) and/or berming the lot and flooding for a short period of time (days to a few weeks)
are some of the more efficient ways to meet the presoaking recommendations. If flooding
- 17-
4971053-001
is performed, a couple of days to let the upper portion of the pad dry out and form a crust
so equipment can be utilized should be anticipated.
5.2.2 Foundation Setback from Slope Face
We recommend a minimum horizontal setback distance from the face of slopes for all
structural foundations, footings, and other settlement-sensitive structures as indicated on
Table 3. This distance is measured from the outside bottom edge of the footing,
horizontally to the slope face and is based on the slope height and type of soil. However,
the foundation setback distance may be revised by the geotechnical consultant on a case-by-
case basis if the geotechnical conditions are different than anticipated.
Table 3
Minimum Foundation Setback from Slope Faces
Slope Height Minimum Recommended Foundation Setback
less than 5 feet
7 feet 5 to 15 feet
5 feet
I greater than 15 feet
within this setback area may be subject to lateral movement andor differential settlement.
Please note that the soils within the structural setback area possess poor lateral stability, and
W2, where H is slope height; not to exceed 10 feet
improvements (such as retaining walls, sidewalks, fences, pavements, etc.) constructed
Potential distress to such improvements may be mitigated by providing a deepened footing
or a pier and grade beam foundation system to support the improvement. The deepened
footing should meet the setback as described above.
4971053-001
5.3 Lateral Earth Pressures and Retaininp. Wall Design Considerations
The recommended lateral pressures for the site soil (expansion index less than 90 per U.B.C. 18-I-B)
and level or sloping backfill are presented on Table 4.
II Table 4 ll
Lateral Earth Pressures
Equivalent Fluid Weight (pcf)
Level Backfill 2:1 Sloping Backfill
Conditions Onsite Soils Onsite Soils
Active 65 40
At-Rest
300 300 Passive
70 60
Embedded structural walls should be designed for lateral earth pressures exerted on them. The
magnitude of these pressures depends on the amount of deformation that the wall can yield under
load. If the wall can yield enough to mobilize the full shear strength of the soil, it can be designed
for "active" pressure. If the wall cannot yield under the applied load, the shear strength of the soil
cannot be mobilized and the earth pressure will be higher. Such walls should be designed for "at-
rest" conditions. If a structure moves toward the soils, the resulting resistance developed by the soil
is the "passive" resistance. The passive earth pressure values assumes sufficient slope setback (see
previous section).
For design purposes, the recommended equivalent fluid pressure for each case for walls founded
above the static ground water and backfilled with import soils of very low to low expansion potential
or onsite (moderately expansive soils) is provided in Table 4. The equivalent fluid pressure values
assume free-draining conditions. If conditions other than those assumed above are anticipated, the
equivalent fluid pressure values should be provided on an individual-case basis by the geotechnical
engineer. Surcharge loading effi from the adjacent structures should be evaluated by the
geotechnical and structural engineer. All retaining wall structures should be provided with
appropriate drainage and appropriately waterproofed. The outlet pipe should be sloped to drain to
a suitable outlet. Typical wall drainage design is illustrated in Figure 3.
For sliding resistance, the friction coefficient of 0.35 may be used at the concrete and soil interface.
In combining the total lateral resistance, the passive pressure or the frictional resistance should be
reduced by 50 percent. Wall footings should be designed in accordance with structural
considerations. The passive resistance value may be increased by one-third when considering loads
of short duration such as wind or seismic loads.
- 19-
4971053-001
Wall back-cut excavations less than 5 feet in height can be made near vertical. For back cuts greater
than 5 feet in height, but less than 15 feet in height, the back cut should be flattened to a gradient
of not steeper than 1: 1 (horizontal to vertical) slope inclination. For back cuts in excess of 15 feet
in excess of 15 feet in height, specific recommendations should be requested from the geotechnical
consultant. The backfill soils (having an expansion index less than 90 per UBC 18-I-B) should be
compacted to at least 90 percent relative compaction (based on ASTM Test Method 01557-91). The
walls should be constructed and backfilled as soon as possible after back-cut excavation. Prolonged
exposure of back-cut slopes may result in some localized slope instability.
Foundations for retaining walls in competent formational soils or properly compacted fill should be
embedded at least 18 inches below lowest adjacent grade. At this depth, an allowable bearing
capacity of 2,000 psf may be assumed.
- 20 -
RETAlNlNQ WALL-
WALL WATERPROOFING PER ARCHITECT'S SPECIFICATIONS
FINISH GRADE
"""""""_"""""""~
" "-"" ~ - - - - - - - FILL<;<;<& -"""
f EQUIVALENT)*
r'PVC PIPE (SCHEDULE 40 OR
4' (MIN.).DlAMETER PERFORATED ~. i EQUIVALENT) WITH PERFORATIONS
WALL FOOTING+^ ;P \
-ll3\ - =Ill - 11 3' MIN.
NOT TO SCALE
CLASS 2 PERMEABLE MATERIAL SPECIFICATIONS FOR CALTRANS
U.S. Standard Sieve Size X Passing
1 " 100
3/8"
3/4" 90-100
No. 4 40-100 25-40 No. 8 No. 30 18-33
No. 50 5-15 0-7 No. 200 0-3
Sand Equivalent>75
\ COMPETENT BEDROCK OR MATERIAL
CONSULTANT
AS EVALUATED BY THE QEOTECHNICAL
*BASED ON ASTM Dl667
**IF CALTRANS CLASS 2 PERMEABLE MATERIAL
(SEE QRADATION TO LEFT) IS USED IN PLACE OF 314'-1-112' QRAVEL, FILTER FABRIC MAY BE DELETED. CALTRANS CLASS 2 PERMEABLE
PERCENT RELATIVE COMPACTION
MATERIAL SHOULD BE COMPACTED TO 00
NOTECOMPOSITE DRAINAGE PRODUCTS SUCH AS MRADRAIN
OR J-DRAIN MAY BE USED AS AN ALTERNATIM TO GRAVEL OR
CLASS 2 INSTALLATION SHOULD BE pEFIFOF4hED IN ACCORDANCE
WlTH MANUFACTURER'S SPECIFICATIONS,
Project No. 4971053-001
RETAINING WALL
EngrJGeol. JGF/RKW DRAINAGE DETAIL
Scale Not to Scale
~~ .. ~~
Drafled By 1042 MQ Figure No 3
4971053-001
5.4 Cement Tvoe for Construction
The soluble sulfate content of the finish grade soils on the site should be determined from
representative samples taken by a representative of Leighton prior to slab construction.
5.5 Private Concrete Drivewavs
To reduce unsightly cracking, the private concrete driveways or alleys should be a minimum 4 inches
thick overlying 2 inches of clean sand (sand equivalent greater than 30), reinforced with 6x6-6/6
welded-wire mesh placed at midheight and provided with weakened plans joints to create relatively
square panels.
5.6 Graded SloDes
It is recommended that any regraded slope within the development be planted with ground cover
vegetation as soon as practical to protect against erosion by reducing runoff velocity. Deep-rooted
vegetation should also be established to protect against surficial slumping. Oversteepening of
existing slopes should be avoided during post-grading and construction unless supported by
appropriately designed retaining structures.
5.7 Control of Surface Water and Drainaee Control
Positive drainage of surface water away from structures is very important. No water should be
allowed to pond adjacent to buildings. Positive drainage may be accomplished by providing drainage
away from buildings at a gradient of at least 2 percent for a distance of at least 5 feet, and further
maintained by a swale or drainage path at a gradient of least 1 percent. Where limited by 5-foot side
yards, drainage should be directed away from foundations for a minimum of 3 feet and into a
collective swale or pipe system. Where necessary, drainage paths may be shortened by use of area
drains and collector pipes. Eave gutters are recommended and reduce water infiltration into the
subgrade soils if the downspouts are properly connected to appropriate outlets.
Planters with open bottoms adjacent to buildings should be avoided, if possible. Planters should not
be designed adjacent to buildings unless provisions for drainage, such as catch basins and pipe
drains, are made. Overwatering of lots should be avoided.
5.8 Preliminarv Pavement Design
Final pavement recommendations should be provided based on R-value testing of the common
driveway subgrade soils once final grades are achieved. However, based on our professional
experience in the Carlsbad area and assuming a Traffic Index of 5.0 and a R-value of 30, a
preliminary pavement section of 4-inches of Asphalt Concrete (A.C.) over 4-inches of Class 2
Aggregate Base material (A.B.) may be assumed for pre-planning purposes only.
- 22 -
4971053-001
The upper 12 inches of subgrade soils should be scarified, moisture conditioned and compacted to
a minimum of 95 percent relative compaction based on ASTM Test Method D1557-91. If fill is
required to reach subgrade design grade, fill placement should be performed in accordance with the
recommendations presented in Section 5.1. The aggregate base material should be compacted to a
minimum of 95 percent relative compaction.
If Portland Cement Concrete (P.C.C.) pavement is planned, we recommend a minimum of 7 inches
of P.C.C. on native soils. The P.C.C. pavement should be provided with appropriate steel
reinforcement and crack-control joints as designed by the project structural engineer. Minimum
reinforcement should consist of No. 3 rebars at 18 inches (on center) at slab midheight which
continues through all crack-control joints but not through expansion joints. If saw-cuts are used, they
should be a minimum depth of 1/4 of the slab thickness and made within 24 hours of concrete
placement. We recommend that sections be as nearly square as possible. A 3,250 psi concrete mix
should be utilized.
Asphalt Concrete, Portland Cement Concrete, and Class 2 Aggregate Base materials should conform
to and be placed in accordance with Carlsbad requirements and the latest revision of the California
Department of Transportation Standard Specifications (Calms) and American Concrete Institute
(ACI) codes.
If pavement areas are adjacent to landscape areas, we recommend steps be taken to prevent the
subgrade soils from becoming saturated. Concrete swales should be designed in roadway or parking
areas subject to concentrated surface runoff. Regular maintenance (such as seal coats and crack
infilling) is an important part of extending pavement life.
5.9 Construction Observation and Testing
The recommendations provided in this report are based on subsurface conditions disclosed by widely
spaced borings and geotechnical analysis. The interpolated subsurface conditions should be checked
in the field during construction by a representative of Leighton and Associates.
Construction observation and testing should also be performed by the geotechnical consultant during
hture grading, excavations, and foundation or retaining wall construction at the site. Grading plans
and final project drawings should be reviewed by this ofice prior to construction.
- 23 -
4971053-001
APPENDIX A
REFERENCES
American Concrete Institute, 1985, Manual of Concrete Practice, Parts 1 and 2.
Benton Engineering, Inc., 1972, Final Report of Compacted Fill Ground and Classification of Soil
Conditions, Lots 413 to 584, inclusive and certain street areas, Las Costa Meadows Unit
No. 3, Carlsbad, California, Project No. 71-7-170, dated October 19, 1972.
Campbell, K.W., 1987, Predicting Strong Ground Motion in Utah, in Assessment of Regional
Earthquake Hazards and Risk Along the Wasatch, Front, Utah, USGS, Open File Report
87-585, Volume 11.
Dawson, Hannouche, Pate Architecture Planning, 1997, Site Plan, Unicornio Homes, T.R.C. Development
Co., 1 Sheet, dated January 25, 1997.
Eisenberg, L.I. and Abbott, P.L., 1985, Eocene Lithofacies and Geologic History, Northern San Diego
County & Abbott, P.L., ed., On the Manner of Deposition of the Eocene Strata in
Northern San Diego County: San Diego Association of Geologists, Field Trip Guidebook,
pp. 19-35.
Hannan, D., 1975, Faulting in the Oceanside, Carlsbad and Vista Areas, Northern San Diego County,
California Ross, A. and Dowlens, R.J., eds., Studies on the Geology of Camp Pendleton
and Western San Diego County, California: San Diego Association of Geologists, pp. 56-
59.
Hart, 1994, Fault-Rupture Hazard Zones in California, Alquist-Priolo Special Studies Zones Act of
1974 with Index to Special Study Zones Maps: Department of Conservation, Division of
Mines and Geology, Special Publication Map No. 1.
International Conference of Building Oficials (ICBO), 1994, Uniform Building Code, Volume I -
Administrative, Fire- and LifsSafety, and Field Inspection Provisions; Volume I1 -
Structural Engineering Design Provisions; and Volume III - Material Testing and
Installation Provisions: ICBO.
Ishihara, K., 1985, Stability of Natural Deposits during Earthquakes, Pm. of the Eleventh
International Conference on Soil Mechanics and Foundation Engineering, San Francisco,
Vol. 1, NO. 7, August 1-16, pp. 321-375.
Jennings, C.W., 1994, Fault Activity Map of California and Adjacent Areas, with Locations and Ages
of Recent Volcanic Eruptions: California Division of Mines and Geology, California
Geologic Data Map Series, Map No. 6,, Scale 1:750,000.
Leighton and Associates, 1992, City of Carlsbad Geotechnical Hazards Analysis and Mapping study,
84 Sheets, dated November, 1992.
,Undated, Unpublished In-House Geotechnical Data.
A- 1
4971053-001
APPENDIX A (Continued)
Rick Engineering Company, 1971, Grading Plans for La Costa Meadows Unit No. 3, 6 Sheets, File No.
188-6A, dated March 12, 1971.
Schnabel, B. and, H.B., 1974, Acceleration in Rock for Earthquakes in the Western United States;
Bulletin of the Seismological Society of America, Vol. 63, No. 2, pp. 501-516, 1974.
Seed, H.B., Idriss, I.M., and Arango, I., 1983, Evaluation of Liquefaction Potential Using Field
Performance Data, Journal of Geotechnical Engineering, ASCE Vol. 109, March,
pp. 282-458.
, 1982, Ground Motions and Soil Liquefaction During Earthquakes, Monogram Series,
Earthquake Engineering Research Institute, Berkeley, California.
, 1971, Simplified Procedure for Evaluating Soil Liquefaction Potential, Journal of Soil
Mechanics and Foundation Division, ASCE Vol. 97, No. SM9, September pp. 1249-1273.
Seed, H.B., Idriss, LM., and Kiefer, F.W., 1969, Characteristics of Rock Motions During Earthquakes,
Journal of Soil Mechanics and Foundations Division, ASCE, Vol. 95, No. SM, Proc. Paper
6783, pp. 1199-1218, September, 1969.
Weber, F.H., 1982, Recent Slope Failures, Ancient Landslides and Related Geology of the Northern-
Central Coastal Area, San Diego County, California: California Division of Mines and
Geology, Open File Report 82-12LA, 77 p.
Ziony, J.I., and Yerkes, R.F., 1985, Evaluating Earthquake and SurfacsFaulting Potential Ziony,
ed., 1985, Evaluating Earthquake Hazards in the Los Angeles Region - An Earth - Science
Perspective: U.S. Geological Survey, Professional Paper 1360, pp. 43-91.
Date
411 1/53
Photo Nos. Flight source
19 and 20 AXN-8M USDA
A-2
GEOTECHNICAL BORING LOG LB-1
Date 3-21-97 Sheet 1 of 2
Project TRCKarlsbad Project No. 4971053-001
Drilling Co. San Diego Drilling Type of Rig Bucket Aue;er
30 in. ~r - Ref. or Datum Mean Sea Level
505Mlll77)
T
WON
GEOTECHNICAL DESCRIPTION
aged BY KBC
impled By KBC
@ 1’: Lght brow. moist, medium dense. clayey silty fine SAND: rootlets common to a depth 2‘. upper 2’ of fdl is loose
@ 5’: Brow to dark brown. mist, medium, silty. flne to dium sandy CLAY: lifts appr tight and moist, lifts are approximately 3-5” thick t
@ 10’: Lght gray-bmw, moist. medium dense, silty tinc to medium SAND I
@ 15’: Light gray-bmm, moist, medium dense, silty furs to medium SAND t
@ 20’: Lght onoge-bmwn, moist, mcdium dense. silty fios to medium SAND
@ 25’: Mixture of dark gray to black. moist, medium dcnse. clayey, silty tine to medium SAND: tine gravel-size inclusions of light blue-gray and light bmm clayey sand wmn: motlets and mots common. organic rich
Hole Diameter 30 ir
~p of Hole
GEOTECHNICAL BORING LOG LB-1
-r
"
"
"
- -
Date 3-21-97 Sheet 2 of 2
Project TRClCarlsbad hject No. 4971053-001
Drilling Co. San Diego Drilling Type of Rig Bucket Auger
1. Drive Weight 0-25' 4,113#, 25'47' 2981# Drop *in.
'1 - ft. Ref. or Datum Mean Sea Level
I
505A1(11/77)
Ul- :! E?
GEOTECHNICAL DESCRIPTION
Zz SampledBy KBC
Lagged By KBC
SM @ 30': Off-white. damp. vev dense, silty fine to medium SANDSTONE. moderately cemented, orange-bmwn imn-axide staining common. few near vertical frachlrcs -
Tolal Depth = 31' Downhole Lo ged to 30' No Gmd dater Encountered at Time of Drilling Backtidled and Tamped on March 21. 1997
I
HTON & ASSOCIATES
GEOTECHNICAL BORING LOG LB-2
" Date 3-21-97 Sheet 1 of 3
Project TRC/Carlsbad Project No. 4971053401
Drilling Co. San Diego Drilling Type of Rig Bucket Auger
- Hole Diameter 30 in. Drive Weight 0-25' 4,113#, 25'47' 2981#, 47'-12' 2.168# Drop ain.
Elevation Tc
.- 505A(lll77)
~p of Hole 503 . ft. Ref. or Datum Mean Sea Level
GEOTECHNICAL DESCRIPTION
;ampled By KBC -
@ 1': Light brown, moist, medium dense, clayey, silty fme SAND, rooflets to I-lI2'. upper 2' is loose and friable
@ 5': Dark brown. moist, stiff, fme mmiy CLAY, lifts generally moist and tight, thiclmesscs range from 4 to 6
@ IO': Light brown, moist, medium dense, clayey, silly fme m medium SAND
@ 15': L t bmwn, moist. mdium dew, clayey, silly fine m medium SA
@ 20': off-white. damp, dense. silly fins SAND, orange-brow nmltles
WmmOU
@ 24': Ligat 0 e-brow and off-white. damp, medium dense. silly fins m
@ 25': Bmwn. moist, stiff. fine dy CLAY
dlum S%D
@ 26': Fine gravels cornon
I
ASSOCIATES
GEOTECHNICAL BORING LOG LB-2
Date 3-21-97 Sheet 2 of 3
Project TRCKarlsbad Project No. 4971053-001
Drilling Co. San Diego Drilling Type of Rig Bucket Auger
Hole Diameter 30 in. Drive Weight 0-25' 4,113#, 25'47' 2981#, 47'-72' 2,168# Drop *in.
Elevation Top of Hole 503 ft. Ref. or Datum
GEOTECHNICAL DESCRIPTION
.~ Mean Sea Level
-aged BY KBC
iampled By KBC
gray silty fme SAND
@ 36'-37': Black organic-rich lift, moist, stiff, fm sandy silty CLAY: organic odor. few wwd hagments
@ 40': Black. moist, sliff, medium sandy CLAY; orgmic-ri&
- @ 50': Light gmy-gncn very dense, silty iine sandy CLAYSTONE . m~entsly h-%R-
t
@ 58': Very light gncn to off-white. very dense, CLAYSTONE CNmbly tcxhlre, imn-oxide std% miss wmmOn
L
ASSOCIATES
GEOTECHNICAL BORING LOG LB-2
I !3Jj GEOTECHNICAL DESCRIPTION
Eo
Date 3-21-97 Sheet 3 of 3
Project TRClCarlsbad Project No. 4971053401
Drilling Co. San Diego Drilling Type of Rig Bucket Auger
Hole Diameter 30 in. Drive Weight 0-25’ 4,113#, 25’47’ 2981#. 47’-12’ 2.168#
Elevation Top of Hole 503 ft. Ref. or Datum Mean Sea Level
Drop &in.
I
i
.
a
GEOTECHNICAL BORING LOG LB-3
Elevation Tc JfHole 48:
'0
ul 0
1 t
t t U
.-
Ref. or Datum
Date 3-21-97 Sheet 1 of 2
Project TRClCarlsbad Project No. 4971053-001
Drilling Co. San Diego Drilling Type of Rig Bucket Auger
Hole Diameter 30 in. Drive Weight - 0-25' 4,113#
Mean Sea Level Drop Xin.
GEOTECHNICAL DESCRIPTION I
BY KBC
jampled By KBC
Elevation Tc
GEOTECHNlCAL BORING LOG LB-4
Date 3-21-97 Sheet 1 of 1
Project TRClCarlsbad Project No. 4971053-001
Drilling Co. San Diego Drilling Type of Rig Bucket Auger
Hole Diameter 30 in. Drive Weight 0-25' 4,113# Drop *in.
tp of Hole 484 ft. Ref. or Datum .~ Mean Sea Level I GEOTECHNICAL DESCRIPTION I
4xed BY KBC
ampled By KBC - @ 0: Li ht gray-green, damp, mepium dense, slightly clayey, silty fme
I""-L-"""L"""""""""" F 63 5": Light green, molst. dense, silty very fme SANDSTONE; orange-brown - SAD. abundant motlets fnablc
imn oxldc stained fractures common, 1/2" thick calcium carbonate ftaCNreS Common -
Total Deoth = 5, Downhoie LO gcd to s No Gmund dter Encountered at Time of Ddli BacLfilcd and Tam@ on March 21, 1997
L
LEIGHTON &ASSOCIATES
GEOTECHNICAL BORING LOG LB-5
Date 3-24-97
Project TRClCarlsbad project No. 4971053-001
Drilling Co. San Diego Drilline.
Hole Diameter 30 in. Drive Weight 0-25' 4,113#
Sheet 1 of 1
Type of Rig Bucket Auger
Drop =in. Elevation Tc ofHole 484
0
m (u
t 5
t +
.-
U
Ref. or Datum Mean Sea Level
I
GEOTECHNICAL DESCRIPTION
,egged BY KBC
lampled By KBC -
@ 1': Light brnwn, moist, loose to medium dense, silly fme SAND; rootlets -
common, upper 1.5' loose -
@ 5': Light gmn. moist. stiff, silty tine +y CLAY; lifts BX generally molst and ught md range from 3 to 5 mches thick
@ 13': kht gmn and brown mixtun. moist. dense. clavev. sil~ fm SANDH
~ app~xufiptsly horizontal, irregular wnkct at bise . .. .
F H - @ IS': Light green, moist, dense, silty fme SANDSTONE owe-brown iron-oxide mining wmmon dong hacturrs. laminrted calcium Earbonate layers wmmon -
-
-
-
- !2 20': OfS-white to very light grccn. damp, vety dense, silty fm to medium SANDSTUNE; iron oxide-miocd blebs wmn
rootal ~~"th = 21' Downhok-h gsd to 19' Yo Ground &ter Eneountersd at Time of Drilling BackfUlcd ami Tlmpcd on Mar& 24. 1997
n USOCIATES
"7 0
u aI
3 + + +
.-
a
GEOTECHNICAL BORING LOG LB-6
Date 3-24-97 Sheet 1 of 1
Project TRCKarlsbad Project No. 4971053401
Drilling Co. San Die0 Drilling Type of Rig Bucket Auger
Hole Diameter 30 in. Drive Weight 0-25' 4,113#
Elevation Top of Hole 486 ft. Ref. or Datum Mean Sea Level
Drop =in.
GEOTECHNICAL DESCRIPTION I
@ 1': Light brown, moist, Iwse to medium dense, clayey, silty fme SAND upper 2' loosc. roofleu common
@ 5': Light brown, moist. medium dense, silty fme m medium SAND. lib arc approximately 4 m 6' thick ud moist and tight
_""""""""""""""""" - @ 11': Light green, damp. dense to very dense, silty fme SANDSTONE; iron oxlde stained vemd hclures wmmon, horizontal laminated calcium ~arbo~te layen u)mmon
No prnctifpl rsMvery of sample
4971053-001
APPENDIX C
Laboratow Testing Procedures and Test Results
Exoansion Index Tests: The expansion potential of selected materials was evaluated by the Expansion
Index Test, U.B.C. Standard No. 18-2. Specimens are molded under a given compactive energy to
approximately the optimum moisture content and approximately 50 percent saturation or approximately
90 percent relative compaction. The prepared 1-inch thick by 4-inch diameter specimens are loaded to
an equivalent 144 psf surcharge and are inundated with tap water until volumetric equilibrium is reached.
The results of these tests are presented in the table below:
II Samole I Samole I Comoacted Drv 1 Exoansion I Exoansion 11
Lot 518 Medium 69 104.9 Clayey Sand (Fill)
Moisture and Densitv Determination Tests: Moisture content and dry density determinations were
performed on relatively undisturbed samples obtained from the test brings. The results of these tests are
presented in the boring logs. Where applicable, only moisture content was determined from "undisturbed"
or disturbed samples.
Hvdroconsolidation: Hydroconsolidation testing was performed by loading representative samples up to
approximate overburden pressure and wetting the sample. The results are presented below:
Sample Location
LB-I, 10'
-0.3 (expansion) LB-I, 5'
Percent Hydroconsolidation
0.03
LB-I, 15'
-0.61 (expansion) LB-5, 5'
-0.03 (expansion)
LB-5, 10' 0.13
LB-6, 5' 0.10
c- 1