1999-6109 G
:p'~~r~ .
we:. ENGINEERS, GEOLOGISTS & ENVIRONMENTAL SCIENTISTS
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GEOTECHNICAL REPORT
FOR
JOYNER RESIDENCE
3113 CAMINO DEL RANCHO
ENCINITAS, CALIFORNIA
Prepared For:
Mr. and Mrs. W.K. Joyner
August 1999
5450 Telegraph Road, Suite 101 0 Ventura, California 93003 0 805-644-2220 0 FAX 805-644-2050
:P. ~ f:l.J.!
i ..- ENGINEERS, GEOLOGISTS & ENVIRONMENTAL SCIENTISTS
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August 6,1999
Project No.: 9903-0130
Mr. and Mrs. W.K. Joyner
P.o. Box 512
Rancho Santa Fe, CA 92067
Subject:
Geotechnical Study, 3113 Camino Del Rancho Property, Encinitas,
Califomia
Dear Mr. and Mrs. Joyner.
Padre Associates, Inc., is pleased to submit this geotechnical report for the
proposed residence at 3113 Camino Del Rancho in Encinitas, California. The report
summarizes the field and laboratory data that were collected for the study and provides
geotechnical recommendations for design and construction of the project.
Padre Associates appreciates this opportunity to provide our services to you and
we look forward to assisting you in the completion of this project. If you have any
questions regarding this study, or if you need additional information, please contact us.
Copies submitted:
Joyner (1)
Chris Light (5)
5450 Tð'!.t~~..~~~~,,~?~~,}.u,¡;~¡,.,falifofnia 93003 0 805-644-2220 0 FAX 805-644-2050
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TABLE OF CONTENTS
TABLE OF CONTENTS.................................................................................................................... i
INTRODUCTION..............................................................................................................................1
STUDY PURPOSE.......................................................................................................................1
PROJECT UNDERSTANDING ....................................................................................................1
WORK PERFORMED ..................................................................................................................1
FINDINGS........................................................................................................................................2
SITE CONDITIONS......................................................................................................................2
Topography...............................................................................................................................2
Drainage Conditions ................................................................................................................. 2
Existing Land Uses...................................................................................................................2
GEOLOGIC CONDITIONS...........................................................................................................3
Regional Geologic Conditions......................................................................................................3
Local Geological Conditions.........................................................................................................3
Geologic Structure .................................................................................................................... 3
Significant Faults ......................................................................................................................3
Groundwater Conditions ...........................................................................................................4
EARTH MATERIALS....................................................................................................................4
Artificial Fill (at) .........................................................................................................................4
Older Alluvium (Qoal) ...............................................................................................................4
ENGINEERING PROPERTIES OF SELECTED EARTH MATERIALS....................................... 4
GEOLOGIC HAZARDS AND SEISMIC DESIGN CONSIDERATIONS........................................... 5
FAULT RUPTURE........................................................................................................................5
LIQUEFACTION ...........................................................................................................................5
SEISMICALLY-INDUCED SETTLEMENT ................................................................................... 5
TSUNAMIS AND SEICHES .........................................................................................................6
LANDSLIDING..............................................................................................................................6
UBC DESIGN RECOMMENDATIONS ........................................................................................5
UBC Seismic Zone Factor ........................................................................................................6
UBC Soil Profile Type ............................................................................................................... 7
UBC Seismic Source Type .......................................................................................................7
UBC Near-Source Factors........................................................................................................ 7
UBC Seismic Coefficient...........................................................................................................7
CONCLUSIONS AND RECOMMENDATIONS ...............................................................................7
GRADING AND EARTHWORK....................................................................................................7
General.....................................................................................................................................7
Building Area Grading............................................................................................................... 8
Materials ...................................................................................................................................8
Site Preparation........................................................................................................................9
Overexcavation.........................................................................................................................9
Fill/Cut Slopes.........................................................................................................................10
FILL MATERIALS AND PLACEMENT ..............."......................... .......................,.................... 10
Fill Materials............................................................................................................................ 10
Engineered Fill........................................................................................................................10
Structural Backfill........................................ ............................................................................11
Utility Trenches, Pipe Bedding, and Trench BackfilL............................................................ 11
Estimated Volume Change.....................................................................................................11
RECOMMENDATIONS FOR SHALLOW FOUNDATION DESIGN........................................... 12
Introduction .............................................................................................................................12
Shallow Footing Design Criteria ............................................................................................. 12
Siabs-On-Grade......................................................................................................................13
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Sliding and Passive Resistance .............................................................................................13
RETAINING WALL DESIGN ...................................................................................................... 14
Active and Passive Pressures ................................................................................................14
Sliding Resistance .................................................................................................................. 14
Backfill Recommendations .....................................................................................................15
ASPHALT PAVEMENT DESIGN ...............................................................................................15
CONCRETE PAVEMENT DESIGN............................................................................................15
CONSTRUCTION MONITORING..................................................................................................16
CLOSURE AND LIMITATIONS ..................................................................................................... 16
REFERENCES CITED...................................................................................................................18
APPENDIX A SUBSURFACE EXPLORATION ............................................................................A-1
APPENDIX B LABORATORY TESTING ......................................................................................B-1
Laboratory Analyses..................................................................................................................B-1
Laboratory Moisture and Density Determinations.....................................................................B-1
Consolidation Test.....................................................................................................................B-1
Compaction ...............................................................................................................................B-1
Shear Strength Tests ................................................................................................................B-2
Expansion Index Test................................................................................................................B-2
PLATES
Plate 1 - Site Location Map
Plate 2 - Geotechnical Map
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INTRODUCTION
This report presents the findings, conclusions, and recommendations of a
preliminary geotechnical study performed for the proposed residence located at 3113
Rancho Del Camino, in Encinitas, Califomia. The proposed site consists of an
approximately 10-acre parcel located approximately 30Q-feet south of the intersection of
Rancho Del Camino and Lone Jack Road. The general site location is shown on Plate 1
- Site Location Map. The services provided for this study were performed in general
accordance with our previous discussions with Mrs. Leslie Joyner and Mr. Chris Light of
C.J. Light Associates.
STUDY PURPOSE
The purpose of this study was to develop preliminary geotechnical
grading and foundation recommendations for the proposed buildings and site work at the
subject property. Our recommendations were developed through exploration and
analysis of the subsurface conditions at the site.
PROJECT UNDERSTANDING
It is our understanding that the proposed primary residence will consist of
an approximately 10,OOO-square-foot, three-level structure with a pool. In addition to the
main residence, an approximately 750-square-foot single-story guest residence is
proposed. The lightly loaded residence and guest house are proposed to be constructed
using wood-frame construction. The buildings are proposed to be supported on shallow
foundation systems.
The proposed main residence will be constructed at varying grades
across the property. The grade differentials across the site will be constructed using
retaining walls with heights of up to about 10 feet. For the purposes of this study, we
have assumed maximum perimeter/wall loads of 10 kips per lineal foot and maximum
column loads of 40 kips. If actual loads are greater than those noted, Padre should be
contacted to reevaluate project recommendations.
In addition, paved driveways, a vehicle entry court and a pond/water
feature will be constructed on site.
WORK PERFORMED
Work tasks performed to complete the geotechnical study included:
Project coordination with Mr. and Mrs. Joyner.
Notification of Underground Service Alert in an effort to locate
underground utilities at the proposed exploration locations;
Drilling, logging, and sampling of six hollow-stem-auger drill holes and
one hand-auger drill hole, and five backhoe test pits at locations within
the proposed buildings, site improvements, and access road
improvements. Locations of the drill holes are shown on Plate 2 -
Geotechnical Map. Logs of drill holes and backhoe test pits are
presented in Appendix A - Subsurface Exploration;
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Laboratory testing of samples obtained from the drill holes. A
description of laboratory tests performed and the results of those tests
are presented in Appendix B - Laboratory Testing.
Discussion with Mr. Chris Light of C.J. Light Associates, to provide
retaining wall design information, and to help select foundation design
criteria;
Evaluation of geotechnical design parameters that can be used by the
project designers; and,
Preparation of this report summarizing the geotechnical data and the
proposed geotechnical design parameters for the building foundations
and site improvements.
Although a brief discussion of geology and faulting is included as part of
this report, this study focused primarily on the development of geotechnical
recommendations for grading and building foundations. A detailed site seismic hazards
analysis is beyond the scope of services for this study. In addition, our proposed scope
of services did not include any services for the evaluation of the presence or absence of
hazardous substances in the soil, ground water, surface water, or atmosphere, or the
presence of any environmentally sensitive habitats, protected species, or culturally
significant areas.
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FINDINGS
SITE CONDITIONS
Topography
The topography of the site is generally characterized by gentle slopes
descending toward the southeast and southwest from an existing building pad cut into
nose of a ridge along the western side of the property. Slopes descend to the southeast
towards a creek/drainage. The slopes immediately above and below the building pad
are inclined at angles ranging from about 5 to 25 degrees. Below those steeper slopes
the slopes become much flatter and are inclined at angles ranging from about 1 to 3
degrees or flatter. Elevations on the property range from about 95 feet above mean sea
level (MSL) near the southeastem comer of the property, to about 130 feet above MSL
at the northwestern corner of the property.
Drainage Conditions
Drainage at the site consists of surface flow to the drainage that runs
along the east side of the property and to a storm drain drop inlet in access road along
the west side of the property.
Existing Land Uses
The property is currently developed with a single family residence and
horse facilities. The existing residence is located on the building pad in the northwest
portion of the site. It is our understanding that this existing residence will be
moved/demolished prior to construction of the new main residence. The remainder of
the property is developed with horse facilities that include stables, barns and riding
arenas.
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GEOLOGIC CONDITIONS
Regional Geologic Conditions
The property is located within the Penn insular Ranges
geomorphic/geologic province of southern California. This province is a northwest-
southeast oriented complex of rocks named for the Penninsular Ranges located east of
the site. The province is composed of sedimentary, igneous, volcanic, and metamorphic
rocks ranging in age from the Holocene to the Mesozoic.
The Penninsular Ranges province in California extends from Mexico north
to the Los Angeles basin, and is bounded to the west by the Pacific Ocean and to the
east by the Mojave Desert geomorphic/geologic province. The province is characterized
by large-scale, northwest-oriented, folding and strike-slip faulting.
Local Geological Conditions
The property is underlain by recent sedimentary colluvium and Eocene-
age claystone deposits overlying Jurassic-age granitic rocks. The colluvium
encountered on site ranged in thickness from about 2 to 6 feet and was composed of
silty clay (Cl), sandy clay (Cl), clayey sand (SC), and silty sand (SM). Generally, the
colluvium was loose to medium dense, and dry to moist. The claystone materials
ranged in thickness from about 2 to 6 feet, was highly weathered to slightly weathered,
dry to moist, with concoidal fractures exposed on recently excavated surfaces. The
granitic rock encountered on site is moderately to highly weathered, moderately to well
indurated, hard, and dry to damp. No groundwater was encountered on site during our
explorations.
Geologic Structure
Geologic structure consists of faulting, folds, bedding planes, and other
structural criteria exhibited by sediments and rocks in the project area. Faulting is
discussed in the Significant Faults section of this report. No significant folds are known
to traverse the site. Geologic units on site were observed to be relatively massive, thus,
bedding orientations of the claystone materials were indistinguishable.
Significant Faults
The State of Califomia designates faults as active, potentially active, and
inactive depending on the recency of movement that can be substantiated for a fault. A
fault is considered active if it can be substantiated that the fault has ruptured during the
Holocene (the last 11,000 years). A fault is considered potentially active if it can be
substantiated that it has ruptured during the Quaternary (the last 2-million years) but not
the Holocene. A fault is considered inactive if it ('.an be substantiated as not having
ruptured within the Quaternary.
The California Division of Mines and Geology (CDMG) evaluates the
activity rating of a fault in fault evaluation reports (FER). FERs compile available
geologic and seismologic data and evaluate if a fault should be zoned as active,
potentially active, or inactive. If an FER evaluates a fault as active, then it is typically
incorporated into a Special Studies Zone in accordance with the Alquist-Priolo
Earthquakes Hazards Act (AP). AP Special Studies Zones require site-specific
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evaluation of fault location and require a structure setback if the fault is found traversing
a project site.
No known faults traverse the site. The closest active fault is the Newport
Inglewood/Rose Canyon fault system, located about 5 miles southwest of the site and
offshore. Other significant, active faults located in the project region include the Palos
Verdes/Coronado bank fault, located about 20 miles to the southwest, and the Elsinor
fault zone, located about 26 miles to the northeast. The San Andreas fault is located
about 70 miles northeast of the site.
Groundwater Conditions
Groundwater was not encountered in any of the drill holes or backhoe test
pits advanced at the site.
EARTH MATERIALS
For this study, we advanced and collected soil samples from six hollow-
stem-auger drill holes (DH-1 through DH-6) and one hand-auger drill hole (DH-7) at the
locations indicated on Plate 2. The drill holes encountered artificial fill materials, older
Alluvium, and geologic formational material.
Artificial Fill (at)
Artificial fill material was encountered in drill holeDH-5 to a depth of about
6 inches. We anticipate that thicker sections of artificial fill materials may exist within the
slope below the house, outside of the locations of our drill holes. We suspect that
artificial fill materials in those areas will consist of the siltstone and claystone units
excavated to create the existing building pad.
Older Alluvium (Qoal)
Older alluvium deposit materials (heretofore discussed as older alluvium)
were encountered from the ground surface to a depths of 8 to 10 feet (DH-1,-2,-3,-5,-
6,and -7). The alluvium materials consisted of interbedded, clayey sand (SC), sandy
clay (Cl), and clay (CH). Granular older alluvium was generally medium dense to dense
and was predominantly fine-grained. Fine-grained older alluvium ranged from stiff to
very stiff, and was locally plastic. Gravel and cobbles were encountered locally
throughout the older alluvium and will likely be encountered during construction.
laboratory test results indicate that the measured dry unit weights typically ranged from
100 to 110 pounds per cubic feet (pcf), and moisture contents ranged from 3 to 16
percent.
ENGINEERING PROPERTIES OF SELECTED EARTH MATERIALS
As part of this study, laboratory testing was performed on selected
samples of earth materials to aid in the assessment of pertinent engineering properties.
The results are included in Appendix B. The laboratory tests include moisture content
and dry density determinations, grain-size analyses, compaction, direct shear,
expansion index (EI), R-value, and one-dimensional consolidation.
The older alluvium/terrace deposits tested range in color from dusky
yellowish brown to moderate brown, to grayish orange, and consist predominately of
sand (SP) to silty sand (SM) with varying amounts of interbedded clay, gravel, and
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cobbles. The granular materials are typically moderately dense to dense and the fine-
grained materials are typically soft to stiff. Cobbles and boulders were observed to
range in maximum width of up to 2 feet in materials encountered on site.
The materials had dry unit weights ranging from about 98 to 124 pounds
per cubic foot (pet) with an average dry unit weight range of about 112 to 118 pet.
Moisture contents ranged from about 4 to 17 percent. Expansion index tests performed
on the older alluvium/terrace deposits found that the material has a medium to high
expansion potential with an EI of 64. Maximum density-optimum moisture content tests
(compaction) on the materials indicates that the materials have a maximum density
range from 123 to 127 pounds per cubic foot (pet) with optimum moisture content ranges
from 10 to 11 percent.
GEOLOGIC HAZARDS AND SEISMIC DESIGN
CONSIDERATIONS
FAULT RUPTURE
The proposed site is not located within an established Alquist-Priolo Fault
Hazard Zone. As noted above, the Rose Canyon fault is the closest known active fault
and it is located about 10 miles southwest of the site and offshore. Because no active or
potentially active faults are known to traverse the site, the likelihood of ground-surface
rupture due to faulting on the proposed site appears to be low.
LIQUEFACTION
Liquefaction is described as the sudden loss of soil shear strength due to
a rapid increase of soil pore water pressures caused by cyclic loading from a seismic
event. In simple terms, it means that a liquefied soil acts more like a fluid than a solid
when shaken during an earthquake. In order for liquefaction to occur, the following are
needed:
Granular soils (sand, silty sand, sandy silt, and some gravels);
A high groundwater table; and
A low density of the granular soils.
Those criteria are not present at the site and it is our opinion that there is
a low potential for liquefaction to occur and adversely effect the proposed structure.
SEISMICALLY-INDUCED SETTLEMENT
Seismically-induced settlement, as used herein, refers to settlement of
unsaturated granular material as a result of densification and particle rearrangement due
to earthquake shaking. Seismically-induced settlement differs from settlement resulting
from liquefaction because there is not a buildup of excess pore water pressure during
the seismic shaking.
Sediments observed at the site were of relatively limited thickness and
overlie granitic rocks. Using the empirical procedure described by Tokimatsu and Seed
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(1987), seismically-induced settlement of those unsaturated granular layers is
anticipated to be less than about one-half inch.
TSUNAMIS AND SEICHES
Tsunamis are large-period sea waves generated by earthquakes and
submarine landslides. Because the project site is located at an elevation of above 100
feet above MSL, it is our opinion that tsunamis have a low potential to adversely impact
the site.
Seiches are oscillations of impounded water bodies due to shaking from a
seismic event. No known water tanks, reservoirs, or impoundments are known to be
located in the vicinity or upstream of the project site. It is our opinion that there is a low
potential for seiches to adversely affect the project site.
LANDSLIDING
The site is a parcel with gently rolling hills. No landslides were observed
on the property during this study. Slopes surrounding the property are relatively
subdued. No landslides were observed on those slopes. It is our opinion that the
potential for landslides to adversely affect the project is low.
Slope failures can occur in temporary excavations made for construction
of the project. Precautions should be taken to reduce the potential for failure of
temporary slopes. Those precautions are discussed in Utility Trenches, Pipe Bedding,
and Trench Backfill section below.
UBC DESIGN RECOMMENDATIONS
At a minimum, structures should be designed in accordance with the
Uniform Building Code (UBe) criteria. USe-based design requires the definition of a
Seismic Zone Factor (Z), a Soil Profile Type (3), Seismic Source Type, Near-Source
Factors (Na and Ny), Seismic Coefficient (Ca and Cy), Site Coefficient Factor (S) and an
Importance Factor (I).
The Structural Engineers Association of Califomia (SEAOC) Commentary
to the UBC indicates that "the primary function of the UBC design requirements are to
provide minimum standards for use in building design regulations to maintain public
safety in the extreme earthquakes....not to limit damage. maintain function, or provide
for easy repair". The owner should note that in the event of severe ground motions,
structures designed per the UBC may be subject to structural damage.
UBC Seismic Zone Factor
The design of structures for seismic loading conditions, in accordance
with the 1997 edition of the UBC, should be based on a Seismic Zone Factor, Z, equal to
0.40. The UBC's Seismic Zone Factor should not be used as an estimate of peak
ground acceleration. If required, peak ground accelerations at the site should be
estimated by performing a site-specific probabilistic or deterministic seismic hazard
analysis.
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UBC Soil Profile Type
The UBC Soil Profile Type, S, is a function of the soil conditions and
subsurface stratigraphy. As noted in this report, the site is underlain by a thin sequence
of medium dense sediments to depths of about 8 feet overlying hard, moderately to well
indurated granitic rocks. We estimate that the site is underlain by a site profile S8, which
corresponds to Rock. In our opinion this soil profile type, of those provided in the UBC,
most closely describes the site conditions.
UBC Seismic Source Type
The UBC Seismic Source Type is based upon the estimated maximum
moment magnitudes and slip rates of faults in the project region. As discussed above, a
number of seismic sources are present in the project region. Based upon the estimated
slip rates and moment magnitudes of the two controlling faults, the Rose Canyon and
Palos Verdes/Coronado Bank faults, we estimate that the Seismic Source Type
conforms to a Type "A". Seismic Source Type A encompasses faults that have the
potential to generate moment magnitudes of at least 7 with a slip rate of greater than 5
millimeters per year. Both faults conform to those criteria.
UBC Near-Source Factors
The UBC Near-Source Factors, N. and Nv, are based upon distance of
the seismic source from the site and the Seismic Source Type. The distance to the Red
Mountain fault is estimated to be about 3,000 feet (920 meters) from the Red Mountain
fault. Using a Seismic Source Type "B" and a distance to the seismic source of less
than 2 kilometers, the following Near-Source Factors are applied:
N.-1.15
Nv - 1AO
UBC Seismic Coefficient
The UBC seismic coefficients, C. and Cv, are based upon the Seismic
Zone Factor, Z, and Soil Profile Type, S. As discussed above, the Seismic Zone Factor
is estimated to be OA and the Soil Profile Type is estimated to be So. using those
criteria, the Seismic Coefficients are estimated to be the following:
C. - OAON.
Cv - OAONv
CONCLUSIONS AND RECOMMENDATIONS
The geotechnical conditions, as encountered in the 7 drill holes and 5
backhoe test pits advanced for this study, indicate that the proposed improvements, as
we currently understand it, can be supported on conventional shallow foundations once
the improvements, as recommended herein, have been completed.
GRADING AND EARTHWORK
General
All grading and earthwork should be performed in accordance with the
City of Encinitas requirements. The following sections provide recommendations for site
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preparation, fill placement, compaction requirements, and construction of utility trenches
and pipe bedding. Also included are anticipated excavation characteristics of the site
materials.
Building Area Grading
Main Residence. The main residence will be constructed in the area of
the existing residential pad. The existing pad will be expanded by cutting the pad down
approximately 8 feet. The main residence shall be supported on shallow foundations
extending down to competent bedrock material as determined by a Padre Geologist.
We anticipate bedrock will be exposed in the pad area but that some foundations along
the southern side of the house may need to be extended to a depth of 3 to 5 feet below
existing grade to reach competent bedrock material.
Pool Area. The pool should be supported on either compacted, non-
expansive fill or competent bedrock. but not both. If competent bedrock is encountered
in the deep end of the pool, the shallow end may need to be overexcavated to
competent bedrock and backfilled with a sand cement slurry up to bottom of pool grade.
The deck area should be constructed by placing non-expansive engineered fill up to
deck grade.
Guest House. The guest house will be constructed on a cut/fill transition
pad. In order to reduce potential differential settlement, the cut side of the pad should be
overexcavated to a depth of 18-inches below bottom of foundations and replaced with
non-expansive engineered fill.
Materials
General Fill. Typically, onsite soils free from organics, debris,
deleterious materials, and oversize materials (I.e., over 3 inches in largest dimension)
are considered suitable for general fill. Soil types that could be encountered within the
anticipated shallow depths of excavation could consist of clayey sand (SC), sandy clay
(Cl), and clay (CH). locally those materials will contain gravel, and cobbles. Onsite
soils were found to be moderately expansive and should not be used within the
proposed building or pool areas.
General Import Fill. Fill materials imported to the site should be free of
organics, trash and debris, deleterious materials, and oversize materials (i.e., over 3
inches in largest dimension). In addition, general imported fill should have an Expansion
Index of less than 30, less than 40 percent passing the No. 200 sieve, and a Plasticity
Index of less than 10. General imported fill should be observed and tested by Padre
prior to being brought to the site.
Pervious Backfill Material. Pervious backfill should be placed behind all
retaining walls to prevent the buildup of hydrostatic pressures. Pervious backfill material
shall meet the requirements specified for Pervious Backfill Material in Section 19 of the
Caltrans Standard Specifications, latest edition.
Structural Backfill Material. Structural backfill material shall meet the
requirements specified for Structural Backfill Material in Section 1 g of the Caltrans
Standard Specifications, latest edition.
Aggregate Base. Aggregate base materials shall conform to
requirements specified for Class 2 Aggregate Base in Section 26-1.02A of the Caltrans
Standard Specifications, latest edition.
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Asphaltic Concrete. Asphaltic concrete shall conform to requirements
specified for Type B asphalt concrete in Section 38 of the Caltrans Standard
Specifications. latest edition.
Filter Fabric. Filter fabric shall consist of a needle-punched nonwoven
geotextile conforming to specifications presented in Section 88-1.03 of the Caltrans
Standard Specifications. latest edition.
Site Preparation
Site preparation for the proposed site improvements should initially
consist of removal and disposal of existing debris. vegetation. tree root systems.
structures. etc. These materials should be removed to expose earth materials that are
free of organics and other deleterious matter. Organic materials should be stripped and
removed from the project site in areas to be graded. We estimate that approximately 1
to 2 inches of surface soil will be removed from the site along with the organic materials.
If buried tanks. abandoned wells. or other underground structures are encountered. they
should be removed or destroyed in accordance with the requirements of the appropriate
regulatory agency. Any resulting excavations should be filled with engineered fill that is
placed and compacted in accordance with the recommendations of the Engineered Fill
Section of this report.
Overexcavation
General. To support the proposed buildings and site improvements. the
areas of proposed improvements should be overexcavated following completion of the
Site Preparation recommendations. Generally. all of the materials encountered are
anticipated to be excavated with conventional earth moving equipment.
The engineer or geologist should observe the resulting overexcavation
surface prior to scarification and recompaction to observe that subsurface conditions are
consistent with those anticipated based on our exploration. If variations in subsurface
conditions are evident. those variations may effect the recommendations contained in
this report.
Guest House. Within the footprint of proposed foundations, and
extending to a minimum distance of 2 feet beyond the foundation footprint. soils should
be overexcavated to a depth of 12-inches below existing grade or 18-inches below
bottom of foundation. whichever is deeper. Once the resulting overexcavation area has
been observed by the engineer or geologist. the exposed surface should be scarified to
a depth of 8 inches. moisture conditioned to near optimum moisture content. and
compacted to a minimum of 92 percent relative compaction (percent of maximum dry
density as determined per standard test method ASTM 01557).
Pavement Areas. Within areas to be paved and extending to a minimum
distance of 2 feet beyond the limits of pavement and curbing, soils should be
overexcavated to a depth of 1 foot below pavement subgrade elevations (bottom of
aggregate base section). Once the resulting overexcavation area has been observed by
the engineer or geologist. the exposed surface should be scarified to a depth of 8
inches. moisture conditioned to near optimum moisture content. and compacted to a
minimum of 90 percent relative compaction. The soil materials should be mixed.
moisture conditioned. and/or removed. as needed. to achieve the recommended
compaction.
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The prepared subgrade should be proof rolled with a loaded water truck
or other heavy pneumatic-tired equipment. Soft or loose areas identified from proof
rolling should be overexcavated and replaced with compacted on-site soils.
We recommend that the subgrade materials be reviewed and tested at
the time of construction to verify the R-value and structural pavement section for those
areas.
Areas to Receive Fill. Areas to receive fill that do not fall within the
Guest House and pavement areas should be overexcavated to a depth of 1 foot below
existing grade. Once the resulting overexcavation area has been observed by the
engineer or geologist, the exposed surface should be scarified, moisture conditioned,
and compacted as recommended for the pavement areas above.
Fill/Cut Slopes
Slopes constructed with fill materials processed and compacted as
discussed above, constructed at slope inclinations of 2:1 (horizontal to vertical) or flatter
are considered to be grossly stable to a maximum vertical height of 15 feet. Cut slopes
into the native materials at inclinations no steeper than 2:1 are considered grossly stable
to a maximum height of 20 feet.
FILL MATERIALS AND PLACEMENT
Descriptions of materials proposed for fills are discussed in the Materials
Section above. Prior to placement of fill, the ground surface to receive fill should be
observed by the engineer or engineering geologist. The ground surface should be
tested where the subgrade has been scarified and compacted. Fill should be placed and
compacted in accordance with the recommendations of the Engineered Fill section of
this report.
Fill Materials
Fill materials and imported fill materials should be used as backfill of
excavations, unless otherwise noted in this report. All imported fill should be observed,
tested if necessary, and approved by the engineer prior to hauling to the site.
When fill material includes rock, large rocks should not be allowed to nest
and form voids within the fill. Therefore, fill material with rock must be carefully placed
so those potential voids are filled with granular fines and properly compacted. Special
mixing operations may be required, depending on the character of the fill materials.
Rocks larger than 6 inches in diameter should not be permitted in the compacted fill.
Engineered Fill
Engineered fill placed in the overexcavation areas, to fill voids left by the
removal of vegetation, tree roots, or utilities, or to bring the site to final grade should be
placed to provide uniform conditions to support the proposed improvements. Fill should
be placed in layers not to exceed 8 inches in loose thickness, and moisture conditioned
as necessary to achieve a moisture content ranging from optimum moisture content to 2
percent above optimum moisture content prior to compaction.
Within building areas and extending to a minimum distance of 5 feet
beyond the foundation footprint, fill should be compacted to at least 92 percent relative
compaction. Within pavement areas fill should be compacted to at least 90 percent
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relative compaction up to within 1-foot of subgrade elevation. The upper one-foot of
pavement subgrade and the aggregate base should be compacted to a minimum of 95
percent relative compaction. Fill placed outside the building and pavement areas should
be compacted to at least 90 percent relative compaction.
Where fills are made on hillsides or exposed slopes inclined steeper than
5 horizontal to 1 vertical (5:1), horizontal benches should be cut into firm, undisturbed,
natural ground. This should provide a horizontal base so that each layer of fill is placed
and compacted on a horizontal plane. The initial bench (key) at the toe of the fill should
be at least 15 feet in width and inclined into the slope. The key should be founded on
competent material as determined by the engineer or engineering geologist The width
and frequency of the succeeding benches will vary with the soil conditions and the
steepness of the slope.
Structural Backfill
Structures should be backfilled with free-draining structural backfill
material. Earth retaining walls that are not designed to support hydrostatic forces should
be constructed with pervious backfill material and weep holes or pipe outlets. The
pervious backfill material should be placed in a one-foot wide zone directly behind the
wall for the entire wall height. Alternatively, a prefabricated drainage panel, such as
Miradrain, should be installed on the back of retaining walls to provide drainage. The
remaining backfill behind structures and retaining walls should consist of structural
backfill material, as described above. Backfill for retaining structures should be
compacted to 90 percent relative compaction. Retaining wall backfill should be placed
within a zone bounded by the back of the wall and a 1: 1 line projected upward from the
heal of the retaining wall footing.
Utility Trenches, Pipe Bedding, and Trench Backfill
Utility trenches greater than 5 feet deep should be braced and shored in
accordance with good construction practice and all applicable safety ordinances. Where
shoring is not used in shallow trenches, we anticipate that some sloughing will occur if
sidewalls are constructed steeper than 1: 1. The actual construction of the trench walls
and worker safety is the responsibility of the contractor.
Pipe bedding for utilities should consist of sand with a minimum sand
equivalent of 30. The sand should extend a minimum of 4 inches below the pipe and 1
foot above the pipe. The bedding material should be compacted to a minimum of 90
percent relative compaction with care given to ensure compaction in the pipeline haunch
area. When placed within areas requiring more stringent compaction requirements, the
higher degree of compaction will govern. Jetting will not be allowed.
Estimated Volume Change
Grading operations will result in volume changes of the on-site earth
materials through shrinkage due to stripping of surface vegetation, and increased
densification of surficial soil due to compaction. The shrinkage losses can be estimated
based on laboratory tests and experience with similar projects. The actual volume
losses will be dependent on construction technique, extent of tree or vegetation root
systems and the accuracy of topographic survey data, all of which can not be accurately
accounted for in the estimate.
Based on our experience, site conditions at the time of our exploration,
and comparisons of in-place dry densities to dry densities at 92 percent compaction, we
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estimate that a shrinkage factor as a result of soil densification of 3 to 7 percent should
be used for design. In addition to soil densification, the loss of approximately 2 inches of
soil across the site as a result of clearing operations should be considered in the
earthwork volume calculations.
RECOMMENDATIONS FOR SHALLOW FOUNDATION DESIGN
Introduction
Shallow foundations and slabs-on-grade may be used for the planned
structures provided the recommendations contained herein (including those for
earthwork and grading presented above) are followed and locally accepted, good quality,
construction techniques are utilized. Shallow foundation elements may consist of
continuous wall footings or isolated spread footings.
Surficial soils encountered within the depths affected by grading vary but
are generally considered to be expansive sandy clay and clay. Because test results
indicate that there is expansive soil present at the site, minimum foundation
requirements for expansive soils and the proposed building types as defined by the UBC
should be considered as minimum requirements for foundation and slab-on-grade
design.
The allowable bearing values recommended below are based on an
evaluation of a safe load that does not result in a shear failure within the soil (i.e.,
maintains an adequate factor of safety against shear failure) or immediate elastic
settlement.
Shallow Footing Design Criteria
Minimum Footing Embedment. We recommend that shallow isolated
and continuous wall footings be founded on either competent bedrock or fill soils
compacted as described above, but not both. The minimum embedment depth relative
to the adjacent finished grade or slab elevation, whichever is lower, should be 24 inches
for perimeter continuous footings, and 18 inches for interior footings.
Minimum Footing Dimension. A minimum footing width of 18-inches is
recommended for both continuous wall and isolated footings. The footing thickness
should be determined by the structural engineer, but should not be less than 12-inches
thick.
Allowable Bearing Pressure. Isolated and continuous wall footing
elements should be proportioned for dead load plus probable maximum live load and a
maximum allowable bearing pressure of 2.000 pounds per square foot (pst) for footings
founded in competent bedrock and 1,500 psf for footings founded in compacted fill. The
allowable bearing pressure can be increased by 300 psf for each additional foot of
footing depth above the minimum recommended. An increase of 150 psf can be added
to the allowable bearing pressure for each additional one-foot of increase in footing
width. However, the maximum allowable bearing pressure should not exceed 3,000 psf.
When considering wind and seismic loads, the allowable bearing pressure may be
increased by one-third. The allowable bearing value is for vertical loads only; eccentric
loads may require an adjustment to the values recommended above.
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Minimum Footing Reinforcement. Footing reinforcement should be
designed by a structural engineer and should conform to pertinent structural code
requirements. Minimum footing reinforcement should not be less than that required for
shrinkage, temperature control, and structural integrity, but should consist of at least four
No.4 bars with two placed at the top, and two placed at the bottom of the footing.
Corrosivity. One soil chemistry (e.g., sulfates, chlorides, resistivity) test
was performed for this study. Results of that test indicate that soils are corrosive to
uncoated ferrous metal and copper pipe. The laboratory test result along with the
corrosion engineer's recommendations for mitigating the effects of soil corrosivity are
included in Appendix B.
Estimated Settlement. Estimated settlements of shallow foundations
supported on a relatively uniform thickness of compacted fill were made using the results
of consolidation tests and estimated building loads (Duncan, J.M., and Buchignani, A.L.,
1976). On the basis of our test results and estimated building loads no greater than 10
kips per lineal foot for continuous footings and 50-kip column loads, we estimate that
total consolidation settlement will be on the order of one inch. Differential settlements for
footings of similar sizes and loading conditions can be assumed equal to one-half of the
total settlement. We expect that up to one-half of the estimated settlements should
occur during construction.
Seismically Induced Settlement Potential. Because the subsurface
soil materials are either fine grained and stiff or are formational units, in our opinion, the
potential for seismically induced settlement is likely to be low.
Siabs-On-Grade
All ground-supported slabs should be designed by a civil engineer to
support the anticipated loading conditions but as a minimum should be at least 4 inches
thick. Reinforcement for floor slabs should be designed by the civil engineer to maintain
structural integrity, and should not be less than that required to meet pertinent code,
shrinkage and temperature requirements, but should be no less than No.4 bars (Grade
60), spaced 18 inches on center each way. Reinforcement should be placed at mid-
thickness of the slab with provisions to ensure it stays in that position during construction
and concrete placement.
Slabs on grade should be constructed on a relatively uniform thickness of
compacted fill. In areas where moisture vapors penetrating the slab may be detrimental
to carpet or linoleum floor coverings, we recommend the placement of a 10-mil thick
visqueen layer placed between two, 2-inch-thick lifts of clean sand below the slab.
Sliding and Passive Resistance
Sliding Resistance. Ultimate sliding resistance generated through a
compacted soil/concrete interface can be computed by multiplying the total dead weight
structural loads by the friction coefficient 0.35.
Passive Resistance. Ultimate passive resistance developed from lateral
bearing of shallow foundation elements bearing against compacted soil surfaces for that
portion of the foundation element extending below a depth of 1 foot below the lowest
adjacent grade can be determined using an equivalent fluid weight of 350 pet.
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Safety Factors. Sliding resistance and passive pressure may be used
together without reduction in conjunction with recommended safety factors outlined
below. A minimum factor of safety of 2.0 is recommended for foundation sliding, where
sliding resistance and passive pressure are used together. The safety factor for sliding
can be reduced to 1.5 if passive pressure is neglected.
RETAINING WALL DESIGN
Active and Passive Pressures
Retaining walls that are free to rotate at least 0.2 percent of the wall
height can be considered unrestrained walls. Unrestrained retaining walls that support
vertical cuts and cantilevered walls less than about 10 feet high can be designed using
equivalent fluid weights of 35 pet and 350 pet for active and passive pressures,
respectively, assuming a horizontal, drained backfill. For design of a retaining wall with
backfill placed at a 2:1 slope above the wall, an equivalent fluid weight of 45 pet should
be used for active earth pressures. Where a uniform vertical surcharge will be present
above the wall, a lateral earth pressure coefficient of 0.5 should be applied to the vertical
surcharge load to compute the increased active pressure on the wall due to the
surcharge.
Restrained retaining walls that support vertical cuts can be designed
using an equivalent fluid weight of 55 pet for at rest pressures, assuming a horizontal,
drained backfill condition. In the event that free draining backfill is not provided behind
retaining walls, Padre should be contacted to provide revised active, at-rest, and passive
pressures for the backfill materials proposed for use.
For the design of a restrained retaining wall with surcharge loads located
within an area that will result in additional lateral load on the wall, the lateral loads should
be determined by multiplying the surcharge load by the appropriate coefficient listed
below. The area in which surcharge loads will result in additional lateral load is the area
behind the top of the wall to a distance x equal to the height of the wall (H).
For a line load Ql: for 1H ~ x ~ 0.7H, use 0.5 Ql.
for 0.7H > x ~ 0.5H, use 0.7 Ql
For a point load Qp: for 1 H ~ x ~ 0.6H, use 0.5 Qp
for 0.6H > x ~ 0.5H, use 0.7 Qp
For an area load q: use 0.5 q
If there are any surcharge point or line loads located within 0.5H feet from
the top of the wall, Padre should be contacted to evaluate the lateral components of
those surcharge loads.
Sliding Resistance
Ultimate sliding resistance generated through a soil/concrete inteñace
can be computed assuming a coefficient of friction of 0.35. Minimum factors of safety of
1.5 and 2.0 are recommended for foundation overturning and sliding, respectively, where
sliding resistance and passive pressure are used together. The safety factor for sliding
can be reduced to 1.5 if passive pressure is neglected.
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Backfill Recommendations
Retaining wall foundations should be supported on a uniform thickness of
compacted fill material prepared according to the recommendations in the Fill Materials
and Placement, and Recommendations for Shallow Foundation design sections of this
report. Backfill behind retaining walls should consist of pervious backfill and structural
backfill materials. Those materials should meet the requirements for Pervious and
Structure Backfill Materials outlined in Section 19 of the Caltrans Standard
Specifications. The pervious backfill material should be placed in a one-foot wide zone
directly behind the wall for the entire wall height. Alternatively, a prefabricated drainage
panel, such as Miradrain, should be installed on the back of retaining walls to provide
drainage. The remaining backfill behind structures and retaining walls should consist of
structural backfill, as described above. Backfill for retaining structures should be
compacted to 95 percent relative compaction. Retaining wall backfill should be placed
within a zone bounded by the back of the wall and a 1: 1 line projected upward from the
heal of the retaining wall footing. Weep holes or subdrains should be incorporated into
the design of retaining structures to keep water pressure forces from acting on the walls.
ASPHALT PAVEMENT DESIGN
R-value tests were not conducted for this study. Samples of the
subgrade materials should be collected upon completion of site grading to confirm the
preliminary estimated asphalt pavement sections presented below. Asphalt pavement
designs were calculated using traffic indices (TI) equal to 4.0 for lightly loaded vehicle
traffic and parking areas, and 5.0 for areas where he:wier truck traffic is anticipated.
Using the conservative R-value of 15 and the traffic indices noted above,
we recommend the following minimum asphalt pavement sections.
TI = 4.0, Light Vehicles, 0.21 ft. asphalt over 0.50 ft. aggregate base.
TI = 5.0. Truck Access, 0.25 ft. asphalt over 0.67 ft. aggregate base.
The preliminary design should be verified at the time of construction by
obtaining R-values from the actual subgrade, and modifications should be made to the
design section if the actual R-values are lower than those assumed for this design. If
possible, granular materials should be placed within road areas during fill placement to
reduce pavement section requirements.
CONCRETE PAVEMENT DESIGN
Preliminary concrete pavement design sections were evaluated using the
American Concrete Institute's Guide for Design and Construction of Concrete Parking
Lots. Report No. 330R-92. assumed traffic loads and the soil "R" value results. The light
vehicles section assumes use by passenger vehicles and lightly loaded pickup traffic
only. The truck access section assumes an average daily truck traffic (ADTT) of 1 and
no single axel loads in excess of 18 kips. The preliminary design sections are as
follows:
Parking Areas --3.5 inches of concrete
Driveways --4.5 inches of concrete
Both sections should be constructed on native soil compacted to a
minimum of 95 percent relative compaction in the upper one foot of subgrade and 6
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inches of aggregate base compacted to 95 percent relative compaction. Concrete
should be designed with a minimum compressive strength of 4,000 psi (pounds per
square inch). Although not required in either section, we recommend the placement of
No.4 reinforcing bars at 18 inches on center, each way, to improve pavement
performance. Contraction joints should be made in the concrete to a depth of at least 1
inch every 10 feet in the driveways. Final concrete pavement design should be verified
based on actual subgrade "R" values and project specific vehicle loads.
CONSTRUCTION MONITORING
The construction process is an integral design component with respect to
the geotechnical aspects of a project. Because geotechnical engineering is inexact,
unanticipated or changed conditions can occur due to the variability of natural process.
Proper engineering and geologic observation and testing during construction are
imperative in allowing the engineer the opportunity to verify assumptions made during
the design process. Therefore, Padre should be retained during site grading and
construction to observe compliance with the design components and geotechnical
recommendations, and to allow design changes in the event that subsurface conditions,
or methods of construction, differ from those anticipated. Padre can conduct the
observation and field testing services, and provide results on a timely basis so that
actions, if necessary, can be taken to mitigate unforeseen changes in subsurface
conditions.
CLOSURE AND LIMITATIONS
This report has been prepared for the exclusive use of Mr. and Mrs. WK
Joyner, and their agents for specific application to the design and construction of the
proposed residence and associated improvements at 3113 Camino Del Rancho, in
Encinitas, California, as shown on Plate 2. Padre prepared the findings, conclusions,
and recommendations presented herein in accordance with generally accepted
geotechnical engineering practices at the time and location that this report was
prepared. No other warranty, express or implied, is made.
Soil and rock materials are typically not homogenous in type, strength,
and other geotechnical properties and can vary between points of observation and
exploration. In addition, groundwater and soil moisture conditions can vary seasonally
and for other reasons. Padre does not and can not have a complete knowledge of the
subsurface conditions underlying a site. The conclusions and recommendations
presented in this report are based upon the findings at the points of exploration,
interpolation and extrapolation of information between and beyond the points of
observation, and are subject to confirmation of the conditions revealed by construction.
If the proposed construction is relocated, redesigned, or should structural
loading be greater than anticipated, the recommendations contained within this report
should be considered invalid unless the changes are reviewed and our
recommendations modified or approved in writing.
We recommend that Padre be retained to review and comment on the
geotechnical aspects of the project and specifications before they are finalized. Also.
the construction process is an integral design component with respect to the
geotechnical aspects of a project. Because geotechnical engineering is inexact,
unanticipated or changed conditions can occur due to the variability of natural process.
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Findings of this report are valid as of the date of issuance; however,
changes in condition of a property can and will occur with the passage of time.
Furthermore. changes in applicable or appropriate standards occur whether they result
from legislation or advancement in technology. Accordingly, findings of this report may
be invalidated wholly or partially by changes outside of our control. This report is subject
to our review and remains valid for a period of one year, unless we issue a written
opinion of its continued applicability thereafter.
The scope of our services did not include any assessment for the
presence or absence of any hazardous/toxic substances in the soil, ground water,
surface water, or atmosphere, or the presence of any environmentally sensitive habitats
or culturally significant areas.
-+-
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REFERENCES CITED
American Concrete Institute, (1992), Guide for Design and Construction
of Concrete Parking Lots, Report No. 330R-92.
Duncan, J.M., and Buchignani, A.L. (1976), An Engineering Manual for
Settlement Studies.
Houston, J.R, and Garcia, AW. (1974), Type 16 Flood Insurance Study:
Tsunami Predictions for Pacific Coastal Communities, U.S. Army Engineers Waterways
Experiment Station, Hydraulics Laboratory, May, 9 p. plus plates and appendices.
Norris, RM., and Webb, RW. (1990), Geology of California, John Wiley &
Sons, New York.
Uniform Building Code (1997), International Conference of Building
Officials.
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JOYNER RESIDENCE
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SITE LOCATION MAP
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APPENDIX A
SUBSURFACE EXPLORATION
The subsurface exploration program for the proposed Joyner Residence
in Encinitas, Califomia, consisted of the advancement of six hollow-stem-auger drill
holes, one hand-auger drill hole, and five backhoe test pits as indicated on Plate 2.
The drill holes were excavated using a truck-mounted CME 75 drill rig
supplied by A & R Drilling of Signal Hill, Califomia. The drill holes were excavated to
depths ranging from 3.5 to 13.5 feet below existing ground surface. All of the drill holes
encountered practical refusal on hard formational material with the exception of drill hole
DH-4. Sampling was performed using a 1-3/8-inch inside diameter (ID) standard
penetration split-spoon sampler (SPT), and a Modified California sampler (2-3/8-inch ID).
The SPT and Modified California samplers were driven by an above-hole, automatic trip
hammer delivering approximately an equivalent amount of driven energy as a 140-pound
safety hammer free-falling from a height of 30 inches. Bulk samples were recovered
from the near-surface drill cuttings.
The backhoe test pits were excavated using a John Deere 410E rubber-
tired backhoe provided by Tim Wycinsky. The test pits were excavated to depths of 8
feet No samples were collected from the backhoe test pits.
The logs of the drill holes and test pits describe the earth materials
encountered, sampling method used, and laboratory tests perfonned. The logs also
show the location, drill hole or test pit number, date of drilling or excavation, and the
names of the logger and drilling/backhoe subcontractor. A Padre engineer or geologist,
using ASTM 2488 for visual soil classification logged the drill holes. The boundaries
between soil types shown on the logs are approximate because the transition between
different soil layers may be gradual and may change with time. The logs of the drill
holes and test pits advanced for this study are presented as Plates A-1 through A-10. A
Key to Terms & Symbols Used on Logs is presented on Plate A-11.
C\MyOocumentJIP""ectDo=nen'SI' ~ 'JOg",'"",,",6' 5
A-1
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