HomeMy WebLinkAbout; El Camino Real Near Chestnut; Preliminary Soils Report; 1989-09-12PRELIMINARY GEOTECHNICAL STUDY
EL WINO REAL NEAR CHESTNUT,
CARISBAD, CALIFORNIA
FOR
MR. PAUL SCHUMAN
C/O SUN HARBOR REALTY
5050 AVENIDA ENCINAS
CARLSBAD, CALIFORNIA 92008
W.O. 1050-SD SEPTEMBER 12, 1989
CeoSoiIs, fnc.
TABLE OF CONTENTS
SITE DESCRIPTION ...................... 1
PROPOSED DEVELOPMENT .................... 2
FIELD EXPLORATION AND EARTH MATERIALS ............ 3
Topsoil ........................ 4
Secondary Seismic Hazards 7 Natural and Cut Slope Stability ............ 8
.............. FAULTING AND REGIONAL SEISMICITY 6 ...............
GROUNDWATER. ........................ 10
LABORATORY TESTING ..................... 10 Compaction Tests .................... 10
Expansion Tests .................... 11
CONCLUSIONS AND RECOMMENDATIONS ............... 11 Slope Stability .................... 12
Lot Capping ...................... 13 Foundation Recommendations ............... 14 Low Expansive Soils .................. 15
Medium Expansive Soils 16
RETAINING WALL DESIGN .................... 18 Bearing Value ..................... 18 Active Earth Pressure ................. 18
Drainage and Slope Maintenance ............. 20
PLANREVIEW.. ....................... 20
LIMITATIONS ......................... 21
.................
Passive Earth Pressures ................ 19
GeoSoits, Znc.
Geotechnical Engineering Engineering Get WY
5751 Palmer Way, Suite D * Carlsbad, California 92008 * [619) 438-3155 * FAX (619) 931-0915
September 11, 1989
W.O. 1050-SD
MR. PAUL SC"
c/o Sun Harbor Realty
5050 Avenida Encinas
Carlsbad, California 92008
Subject: Preliminary Geotechnical Study El Camino Real near Chestnut, Carlsbad, California
Dear Mr. Schuman:
This report presents the results of our preliminary geotechnical
evaluation of the subject property. The purpose of this study
was to evaluate geotechnical conditions onsite relative to the
proposed construction of 14 multi-family residence structures and
an access road. Pertinent field data are shown on the Geologic
Map enclosed as Plate 1 which utilizes a 1 inch= 30 foot scale
map, prepared by Frederick Engineering as a base.
SITE DESCRIPTION
The subject property is a rectangular shaped parcel located on
the east side of El Camino Real near Chestnut in the City of
Carlsbad, California. The site is in part, a relatively flat pad
area that descends on the west to El Camino Real. Drainage on
the pad area flows irregularly to the south and down slopes to
Los Angeles Co. (818) 785-2158 f Omnge Co. (714) 647-0277 Riverside Co. (714) 677-9651
MR. PAUL SCHUMAN
W.O. 1050-SD
SEPTEMBER 12, 1989
PAGE 2
the west and south. Ruins of a small structure currently occupy
the site. The existing pad area is sparsely vegetated while
some more mature landscaping, consisting of shrubs and grass,
exist on lower slope areas adjacent El Camino Real.
Essentially the entire site has been previously grading, either
during grading of an old airfield or in conjunction with grading
for the construction El Camino Real.
PROPOSED DEVELOPMENT
It is our understanding that grading plans for the site have not
been prepared and the extent of additional grading is unknown. A
topography map of the site has been transmitted to GeoSoils, Inc.
It is our understanding based on discussions with Frederick
Engineering that 14 multi-family structures are to be constructed
with associated driveway access. Grading plans should be
submitted to this office for review and comment as they become
available, to minimize any misunderstanding between the plans and
recommendations contained herein. If conditions are found to
differ substantially from those stated, appropriate
recommendations would be offered at that time.
GeoSoils, Inc.
HR. PAUL Sm
W.O. 1050-SD
SITE STUDIES
SEPTWBER 12, 1989 PAGE 3
Our field studies were conducted between July and August, 1989.
Efforts undertaken in order to prepare this report are:
1. Geologic mapping of available outcrops and exposures both on and near the project.
2. Studies of stereoscopic aerial photographs of the project
3. The excavation of eleven exploratory test pits throughout
4. Laboratory testing and analyses considered representative of
5. A review of published geologic literature on the surrounding
area.
the property.
on site materials.
area.
Other appropriate geologic and soils engineering analyses. 6.
FIELD EXPLORATION AND EARTH MATERIAIS
Subsurface conditions were explored by excavating eleven (11)
exploratory test pits. Exploratory trenches ranged from 1 to 15
feet in depth. Logs of the trenches are included in this report
as Appendix A. Field exploration was performed on July 27, 1989
by our staff geologist who logged the exploratory trenches, and
obtained bulk samples of representative site materials for
laboratory testing. The approximate location of the exploratory
trenches are indicated on the enclosed Geologic Map, Plate 1.
Geologic cross sections are presented on Plate 2.
GeoSofls, Inc.
MR. PAUL Sc"
W.O. 1050-SD
SEPTEMBER 12, 1989 PAGE 4
Earth materials on the subject property include debris-laiden
fill soils that have been dumped on the site over a number of
years. This fill covers approximately the southern two-thirds of
the site and is at least 15 feet in thickness in some locations
and appears to have a maximum thickness on the order of 20 feet.
The soils are dominantly red brown and dark brown silty and
clayey sand.
Excavations into these fill soils and observations of these soils
on the face of fill slopes revealed significant amounts of
concrete, metal pipe and asphalt as well as various
concentrations of wood, broken glass and miscellaneous debris.
Fill soils were predominantly loose and dry throughout, with
caving of the exploratory pits common. This fill is not
considered suitable for structural support and should be
completely removed in areas to be graded. Reuse of these soils
would be difficult due to the rather high percentage of debris
present.
TODSOil
Limited accumulations of topsoil were encountered on natural
slope faces adjacent El Camino Real. These surficial soils are
dark brown in color and composed of medium to coarse sandy clay
that is soft to medium stiff, porous and dry. Rootlets are
common. Where encountered, topsoil ranged in thickness from 1 to
2+ feet. Topsoil was not encountered on the upper flat pad (as
GeoSolls, Znc.
MR. PAUL SCHUMAN
W.O. 1050-SD
SEPTEMBER 12, 1989
PAGE 5
it was previously removed) or in any tests pits, but may be
present beneath areas of the fill. Topsoil is not considered
suitable for support of structures or fill but is suitable for
reuse as compacted fill.
Cobbles and sands of the Quaternary Linda Vista Formation form a
cap on the higher portions of the site. On site, these terrace
deposits were observed to range from approximately 1 to 5 feet in
thickness. The cobbles are set in a stiff sandy clay matrix
while the sands are well indurated and occasionally cemented.
Linda Vista Formation appears limited to the area above
elevations 280 to 285.
The Eocene Santiago Formation is the oldest sedimentary unit on
the property. It underlies the Linda Vista Formation, portions
of the fill, or is present on existing cut slopes and natural
slopes. On site, the Santiago Formation consists principally of
massively bedded, pale brownish gray to white coarse sandstone.
One fairly distinct 1 to 2 foot thick mudstone bed is present.
The dominant bedding orientations vary from northwest and
southwest with westerly dips of 4 to 6 degrees. Some north
trending high angle joint sets were also observed in the cut
slope adjacent El Camino Real.
In general, both the Linda Vista Formation and the Santiago
Formation are considered suitable for support of structures and
GeoSoils, Inc.
MR. PAUL SC"
W.O. 1050-SD
SEPTEMBER 12, 1989 PAGE 6
fill. However, the bedding structure combined with the mudstone
of the Santiago Formation can effect slope stability.
FAULTING AND REGIONAL SEISMICITY
Faults are known to have affected the older basement rocks of the
Peninsular Range Province. A small fault has been tentatively
located by Weber, 1982, beneath El Camino Real at Chestnut. No
evidence of this fault was observed on site. Occasional bedrock
fracture planes (jointing) were observed in road cut exposures.
While no active or potentially active faults were mapped within
or in proximity to the subject property, there are a number of
faults in the Southern California area which are considered
active and which would have an effect on the site in the form of
ground shaking, should they be the source of an earthquake.
The San Jacinto Fault seems to be the most consistently active
zone within a 100 mile radius of the subject site, and of course
the San Andreas is the largest fault zone in California. The
Rose Canyon Fault zone represents the closest possibly active (as
suggested by recent studies) La Nacion Fault is generally
considered as potentially active.
The possibility of ground acceleration at the site may be
considered as approximately similar to the probability for the
GeoSoSts, Znc.
MR. PAUL SC"
W.O. 1050-SD
SEPTEMBER 12, 1989 PAGE 7
Southern California region as a whole. The relationship of the
site location to the major mapped faults within Southern
California is indicated on the Fault Map of Southern California,
Figure 1 and distances to major faults are shown on Table 1
below. Assuming a magnitude 7.0 earthquake on the Rose Canyon
Fault 6 miles from the site, repeatable high acceleration (MA)
(Ploessel and Slosson, 1974) would likely not exceed 0.31 at the
site. This size of event on the Rose Canyon Fault is, in our
opinion, unlikely and the other active faults listed in Table 1
are considered more probable to effect the site give known
seismicity of the various faults.
TABLE 1
Fault
Rose Canyon Coronado Banks Elsinore La Nacion
San Jacinto San Andreas
Miles from Site
6
21
25
32
48
74
Secondarv Seismic Hazards
Surface Fault Rupture:
As no active or possibly active faults were identified within the
site vicinity during our subsurface exploration investigations,
the hazard from surface fault rupture of active faults appears
very low. However, due to the proximity of known active faults
and possible active faults, moderate to severe ground shaking may
reasonably be expected during the life of the development.
GeoSoils, Inc.
Modified after Friedman and Others, 1976
I FAULT MAP
MR. PAUL SC"
W.0. 1050-SD
SEPTEMBER 12, 1989 PAGE 8
Ground Lurching, or Shallow Ground Rupture: Ground lurching or
shallow ground rupture occur as a result of strong, earthquake
induced ground shaking. The phenomenon often occurs along
contacts between material types with contrasting physical
properties (e.g., fill versus hard rock). It can also occur
along pre-existing planes of weakness (i.e., bedding planes,
joint/fracture systems, or inactive faults). While this
potential exists it is our opinion that it is very low and that
the subject property is at no greater risk from this phenomenon
than other nearby property given similar site conditions.
Other Hazards Considered: The following listing includes other
seismic related hazards that have been considered for our
evaluation of the site. These hazards are considered negligible
and/or completely mitigated as a result of site conditions and
typical site development procedures:
* Seiche
* Liquefaction
* Seismic settlement or consolidation
* Potential for tsunamis
Natural and Cut SloDe Stability
The existing slope along the western limits of the property
displays a variety of gradients and geologic conditions. Natural
GeoSofIs, ha.
HR. PAUL SC"
W.O. 1050-SD
SEPTEMBER 12, 1989 PAGE 9
slope area of the southwest corner of the pxoperty is mantled by
topsoil and rises from El Camino Real at approximately a 4:l
gradient (horizontal to vertical). Cut slope in the northwest
corner of the property rises steeply at approximately a 3/4:1
gradient and has an overhanging ledge at the top in the Linda
Vista Formation.
Bedding within the Santiago Formation dips westward, displaying
components that are slightly adverse to west facing slopes. The
sediments are predominantly sandstones with a distinct mudstone
interbed. Groups of near vertical joints (fractures) were also
encountered, trending sub-parallel to the western slopes.
Gross stability of the cut slope area adjacent El Camino Real is
likely to be affected by several of the geologic conditions
mentioned above, including 1) adverse bedding conditions, 2)
mudstone within cut slope, and 3) vertical fractures sub-parallel
and in near proximity to existing slope face. Additionally, it
has been noted that landscaping irrigation can markedly increase
sub-surface water. These waters can perch on mudstone beds and
effect the gross stability of nearby slopes.
While the gentler natural slope is relatively stable in regards
to erosional processes, the steep cut slope is undergoing rapid
erosion. Continued undermining of the overhanging ledge will
increase the hazard of block failure upon the street below.
GeoSoils, Inc.
MR. PAUL SCHUMAN
W.O. 1050-SD
GROUNDWATER
SEPTEMBER 12, 1989 PAGE 10
Groundwater was not encountered in our test trenches, and there
is no evidence of near-surface groundwater on or in the immediate
vicinity of the site. Groundwater is not anticipated to affect
site development. It should be noted however, that fluctuations
in the level of the groundwater may occur due to variations in
rainfall, temperature and other factors not evident at the time
measurements were made and reported herein.
LABORATORY TESTING
Comaction Tests
To determine the compaction character of site soils, compaction
testing was performed on representative samples of near surface
materials. Testing was performed in accordance with ASTM Test D-
1557-78. Laboratory maximum dry densities and an optimum
moisture contents are listed below.
Soil ~vr, e Maximum Optimum Dm Density % Moisture %
A-Light tan silty coarse sand 121.0 B-Light brown silty fine sand 119.0 C-Brown coarse sandy clay 116.0
11.5
13.5
15.0
GeoSoils, Inc.
KR. PAUL SC"
W.O. 1050-SD SEPTEMBER 12, 1989 PAGE 11
Emansion Tests
Swell tests were performed on a remolded samples of near surface
soils. A swell test was also performed on a sample of topsoil.
Samples were prepared at 80 percent of the optimum moisture and
at 90 percent of the maximum dry density, placed under a 60 pound
per square foot surcharge, and submerged in water for 24 hours.
The percent swell was then recorded as the amount of vertical
rise compared to the original one inch sample height. The
results of the test are presented below.
Test Pit DeDth (ft.1 Percent Swell Expansion Potential
TP-7 2
TP-10 1 Topso i 1 0
3.5
3.5
19.0
LOW
Low Critical
CONCLUSIONS AND RECOMMENDATIONS
Based on our field exploration, laboratory testing and
engineering and geological analysis, it is our opinion that the
project site is suited for the proposed development from a soils
engineering and geologic viewpoint, provided that the
recommendations presented below are incorporated into the final
design, grading and construction phases of development. The
items having the most impact on site development from our
viewpoint are: 1) presence of the existing fill, 2) presence
GeoSoils, Inc.
MR. PAUL SC"AN
W.O. 1050-SD
SEPTEMBER 12, 1989
PAGE 12
of slightly adverse mudstone, and 3) the existing steep cut
slopes.
The recommendations offered assume grading to create level
building pads is performed. If this is not done, additional
recommendations should be requested.
Grading
Removals:
Prior to placing fill, old fill and surficial soil deposits
(topsoils) should be removed to competent underlying materials.
Removal operations should be observed by our representative.
Removal depths for old fill will likely exceed 15 feet along the
western side of the fill. Depths on the order of 20 feet and
possibly deeper are anticipated. The upper one foot of bedrock
will also likely need reprocessing.
Removal depths where topsoil is encountered should generally be
on the order of 1 to 2 feet. Locally deeper removals of
topsoil/colluvium should be anticipated in swale areas.
Slope Stability
Although grading plans are not prepared at this time, it is our
opinion that stabilization efforts of some sort will need to be
incorporated into final design plans for all of the cut slope
area adjacent El Camino Real. The efforts might include design
GeoSoils, Inc.
PEL PAUL SC"
W.O. 1050-SD
SEPTEMBER 12, 1989
PAGE 13
of retaining wall, crib wall, slope buttressing, or other designs
for review and comment. Appropriate recommendations would be
offered at such time as the initial site grading plans are
available and submitted to GeoSoils, Inc. for review and comment.
All graded slopes should be designed and graded at no steeper
than a 2:l gradient (horizontal to vertical). Should any adverse
geologic conditions be encountered during grading of cut slopes,
possible remedial grading recommendations would be considered at
that time. Fill slopes up to 10 feet high should be grossly
stable, provided grading is performed in accordance with the
grading guidelines. If higher slopes are anticipated, they
should be specifically reviewed by this office.
Lot Cappinq
Although finish pad elevations are not known at this time, it is
likely that transition pads will be created during grading (cut
and fill within the same lot). In order to provide more uniform
foundation support conditions, it is recommended that the cut
portion of transition pads be overexcavated a minimum of 3 feet
below finish grade and be replaced with a fill cap. The need to
cap lots should be evaluated during grading as some cut lots also
may exhibit materials with significantly different expansive
potentials (e.g. sandstone and mudstone). Slope stabilization
may also create a transition condition above the slope.
GeoSoils, Inc.
KR. PAUL SC”
W.O. 1050-SD
SEPTEMBER 12, 1989
PAGE 14
Foundation Recommendations
Based on our observations and test results, it is anticipated
that low and medium expansive soils would be exposed at finished
grades. It should be fairly easy to avoid high to very highly
expansive soil being present within 3 foot of finish grade.
Although not grading plans currently exist, both cut and fill
lots are anticipated to constructed. Preliminary recommendations
for foundation construction are presented below. The specific
criteria to use for each lot or building pads should be based on
evaluation and expansion testing performed after grading is
complete.
Design:
1. An allowable soil bearing pressure of 1,500 pounds per square
foot may be used for the design of continuous footings with a
minimum width of 12 inches and depth of 12 inches. The
bearing pressure may be increased by one-third for seismic or
other temporary loads.
2. An allowable coefficient of friction between concrete and
compacted fill or bedrock of 0.4 may be used with the
deadload forces.
3. All footings adjacent to descending slope should be deepened
to provide a minimum horizontal distance for the bottom edge
of the footings to the slope face. The set back from the
GeoSoils, Inc.
MR. PAUL SC"
W.O. 1050-SD
SEPTEMBER 12, 1989
PAGE 15
slope face should be equal to one third of the vertical
height of the slope with a minimum of 7 feet to a maximum of
20 feet. This is not intended to supercede any required
building clearance from slopes as set forth by the City of
Carlsbad or the Uniform Building Code.
Construction:
The following recommendations may be applied to construction of
foundations for typical one and two story slab-on-grade, wood
frame residential structures, based upon anticipation that low to
moderately expansive materials may be present at finish grades.
Low Exuansive Soils
1. Footings may be constructed according to standard building
code requirements regarding width and depth. No
reinforcement is necessary due to expansion. However, it is
recommended placing two No. 4 reinforcing bars one near the
top and one near the bottom of footings be used.
2. Concrete slabs, where moisture condensation is undesirable,
should be underlain with a vapor barrier consisting of a
minimum of six mil polyvinyl chloride or equivalent membrane
with all laps sealed. This membrane should be covered with a
minimum of one inch of sand to aid in uniform curing of the
concrete.
CeoSoils, Inc.
MR. PAUL Sc"
W.O. 1050-SD
SEPTEMBER 12, 1989 PAGE 16
3. Concrete slabs, except in garage areas, should be reinforced
with six inch by six inch, No. 10 by No. 10 welded wire mesh.
All slab reinforcement should be supported to ensure proper
positioning during placement of concrete. Garage slabs
should be poured separately from the residence footings. A
positive separation should be maintained with expansion joint
material to permit relative movement.
4. No specific presaturation is required, however, footing
trenches and soil at pad grade should be well watered prior
to pouring concrete.
Medium Emansive Soils
1.
2.
3.
Exterior footings should be founded at a minimum depth of 18
inches below the lowest adjacent ground surface. Interior
footings may be founded at a depth of 12 inches below the
lowest adjacent ground surface. All footings should be
reinforced with two No. 4 reinforcing bars, one placed near
the top and one placed near the bottom of the footing.
A grade beam, reinforced as above, and at least 12 inches
wide should be provided across garage entrances. The base
of the grade beam should be at the same elevation as the
bottom of adjoining footings.
Concrete slabs, where moisture condensation is undesirable,
should be underlain with a vapor barrier consisting of a
GeoSoils, fnc.
MR. PAUL SC"
W.O. 1050-SD
SEPTEMBER 12, 1989
PAGE 17
minimum of six mil polyvinyl chloride or equivalent membrane
with all laps sealed. This membrane should be covered with a
minimum of one inch of sand to aid in uniform curing of the
concrete.
4. Concrete slabs, except in garage areas, should be reinforced
with six inch by six inch, NO. 10 by No. 10 welded wire mesh.
All slab reinforcement should be supported to ensure
placement near the vertical midpoint of the concrete.
5. Garage slabs need not be reinforced with the above criteria;
however, they should be poured separately from the residence
footings and be quartered with expansion joints or saw cuts.
A positive separation from the footings should be maintained
with expansion joint material to permit relative movement.
6. Presaturation is recommended for these soil conditions. The
moisture content of the subgrade soils should be equal to or
greater than optimum moisture to a depth of 18 inches below
grade in the slab areas and verified by this office within
48 hours of pouring slabs and prior to placing visqueen or
reinforcement.
GeoSoils, fnc.
MR. PAUL SC"
W.O. 1050-SD
RETAINING WALL DESIGN
SEPTEMBER 12, 1989 PAGE 18
The recommendations presented below are for cantilevered
retaining walls up to 15 feet high, backfilled with low expansive
granular backfill.
All retaining walls should be provided with an adequate backdrain
system, to prevent buildup of hydrostatic pressures and be
designed in accordance with minimum standards of the City of
Oceanside. In addition, gravel used in backdrain systems should
be a minimum of 12 inches of Class I1 filter material or clean
crushed rock wrapped in filter fabric. Retaining walls should be
backfilled with properly compacted fill, allowing a minimum two
foot thick compacted fill blanket of native material at the
surface. Proper surface drainage should also be provided.
warins Value
An allowable bearing capacity of 1,500 pounds per square foot in
compacted fill and 2,500 psf in bedrock may be used for retaining
wall footing design provided the footing is at least twelve
inches below the ground surface at the toe. Increases may be
allowed in certain areas.
Active Earth Pressure
Active earth pressure may be used for retaining wall design,
provided the top of the wall is not restrained from minor
CeoSolls, Inc.
MR. PAUL SC"
W.O. 1050-SD
SEPTEMBER 12, 1989
PAGE 19
deflections. An equivalent fluid pressure approach may be used
to compute the horizontal pressure against the wall. Appropriate
fluid unit weights are given below for specific slope gradients
of the retained material. These to not include other
superimposed loading conditions such as traffic, structures,
seismic events or adverse geologic conditions (i.e. cut slope
adjacent to El Camino Real). Active earth pressure
recommendations for expansive soils can be determined by specific
laboratory testing of on-site materials.
Surface Slope of Retained Material Horizontal to Vertical
Level 5 to 1
4 to 1
3 to 1
2 to 1
Equivalent Fluid Weight
P.C.F.
30
32
35
38
43
Passive Earth Pressures
1. Passive earth pressure may similarly be computed using an
equivalent fluid unit weight of 200 pounds per cubic foot
with a maximum earth pressure of 2,000 pounds per square
foot .
2. An allowable coefficient of friction between soil and
concrete of 0.4 may be used with dead load forces.
GeoSofb, Inc.
MR. PAUL SCHUl4A.N
W.O. 1050-SD
SEPTEMBER 12, 1989
PAGE 20
3. When combining passive earth pressure and frictional
resistance, the passive pressure component should be reduced
by one-third.
Drainase and SloDe Maintenance
Positive drainage should be maintained away from all foundations
and slopes. Ponding should not be allowed. All drainage should
be conducted to the street or other approved facility.
Water has been shown to weaken the inherent strength of all earth
materials. Slope stability is significantly reduced by overly
wet conditions. Positive surface drainage away from graded
slopes should be maintained and only the amount of irrigation
necessary to sustain plant life should be provided for landscaped
areas. Overwatering should be not be allowed to occur.
PLAN REVIEW
Specific grading plans should be submitted to this office for
review and comment as they become available, to minimize any
misunderstandings between the plans and recommendations presented
herein. In addition, foundation excavations and earthwork
construction performed on the site should be observed and tested
by this office.
from those stated, appropriate recommendations would be offered
at that time.
If conditions are found to differ substantially
CeoSo#ls, Inc.
MR. PAUL Sc"
W.O. 1050-SD
LIMITATIONS
SEPTEMBER 12, 1989
PAGE 21
The materials encountered on the project site and utilized in our
laboratory study are believed to representative of the total
area. However, variations from the anticipated conditions and
actual field conditions should be expected. Test excavations are
reflective of the soil and rock materials only at the specific
location explored. Site conditions may vary due to seasonal
changes or other factors.
Since our study is based on the site materials observed,
selective laboratory testing and engineering analyses, the
conclusions and recommendations are professional opinions based
upon those parameters. These opinions have been derived in
accordance with the current standards of practice and no warranty
is expressed or implied. Standards of practice are subject to
change in time.
CeoSolls, Inc.
MR. PAUL SC"
W.O. 1050-SD SEPTEMBER 12, PAGE 22
1989
If you should have any questions regarding tl
not hesitate to contact this office.
Respectfully submitted,
GeoSoils, Inc. n
Michael A. McDowelf Vithyya Singhanet-- Staff Geologist Hotechnical Engineer
Principii Geologiz
MAM/VS/TEM/mlc
Enclosures: Appendix A, Test Pit Logs Appendix B, Grading Guidelines Plate 1, Geologic Map Plate 2, Geologic Cross Sections
Distribution: (6) Addressee
GeoSoils, Znc.
REFERENCES
Ploessel, Michael R. and Slosson, James E., 1974, Repeatable High Ground accelerations - Important Design Criteria; California Geology, September, p. 195-199.
Weber, Harold F., Jr., 1982, Geologic Map of the Central - North Coastal area of San Diego County, California, showing recent slope failures and pre-development landslides: Cal. Div. of Mines and Geology, Open-File Rpt. 82-12 LA Noxth-Coastal for San Diego County Area - Plate 1.
GeoSoils, Inc.
APPENDIX A
TEST PIT LOG
GeoSoils, Znc.
TEST PIT LOG
Location Deuth fft.)
TP-1 0-12
12+
Haterial Pill
FILL: Red brown silty sand with abundant debris (concrete, pipe,
glass, wood) loose, dry, caving in trench.
BEDROCK - SANTIAGO FORMATION: Light brown gray medium coarse SANDSTONE, slightly clayey medium dense, slightly moist.
Total Depth= 12
TP-2 0-2 pILL: Red brown silty sand with abundant debris (concrete, pipe, glass, wood) loose, dry, caving in trench.
2-4
4+
BEDROCK - LINDA VISTA FORMATION:
Red brown sandy Clay with
feldspar mineral grains, medium stiff, slightly moist with 2-3"
cobble at base.
BEDROCK - SANTIAGO FORMATION: Light brown gray medium coarse SANDSTONE, slightly clayey medium dense, slightly moist.
Total Depth= 4 Feet
TP-3 0-4
4-5
5+
FILL: Red brown silty sand with abundant debris (concrete, pipe, glass, wood) loose, dry, caving in trench.
BEDROCK - LINDA VISTA FORWITION: Red brown sandy clay with feldspar mineral grains, medium stiff, slightly moist with 2-3" cobble at base.
BEDROCK - SANTIAGO FORMATION: Light brown gray medium coarse SANDSTONE, slightly clayey medium dense, slightly moist.
Total Depth= 5 Feet
GeoSoffs, Inc.
MR, PAUL SC"
W.O. 1050-SD
TP-4 0-11
11+
AUGUST 1989
TEST PIT LOG
Material Fill
u: Red brown silty sand with abundant debris (concrete, pipe,
glass, wood) loose, dry, caving in trench.
BEDROCK - SANTIAGO FORMATION: Light brown gray medium coarse SANDSTONE, slightly clayey medium dense, slightly moist.
Total Depth= 11 Feet
TP-5 0-0.5 u: Red brown silty sand with abundant debris (concrete, pipe,
glass, wood) loose, dry, caving
in trench.
0.5-3 BEDROCK - LINDA VISTA FORMATION: Abundant cobbles (2-4") in red brown clayey Sand and sandy Clay matrix.
4+ BEDROCK - SANTIAGO FORMATION: Light brown gray medium coarse SANDSTONE, slightly clayey medium dense, slightly moist.
Total Depth= 3 Feet
TP-6 0-15 FILL: Red brown silty sand with abundant debris (concrete, pipe, glass, wood) loose, dry, caving in trench.
15+ BEDROCK - SANTIAGO FORMATION: Light brown gray medium coarse SANDSTONE, slightly clayey medium dense, slightly moist.
Total Depth= 15 Feet
GeoSofts, Inc.
MR. PAUL SCHU"
W.O. 1050-SD
Location kDth fft.1
TP-7 0-1
1-2.5
AUGUST 1989
TEST PIT LOG
Material Fill
BEDROCK - LINDA VISTA FORMATION:
Abundant cobbles (2-4") in red brown clayey Sand and sandy Clay
matrix.
BEDROCK - SANTIAGO FORMATION:
Light brown gray medium coarse SANDSTONE, slightly clayey medium dense, slightly moist.
Total Depth= 2.5 Feet
TP-8 0-6
6-7
lf
w: Red brown silty sand with abundant debris (concrete, pipe,
glass, wood) loose, dry, caving in trench.
BEDROCK - LINDA VISTA FORMATION:
Red brown sandy Clay with mineral fragments, slightly moist.
Light brown gray medium coarse
SANDSTONE, slightly clayey medium dense, slightly moist.
Total Depth= 7 Feet
BEDROCK - SANTIAGO FORMATION:
GeoSolls, Inc.
MR. PAULSC"
W.O. 1050-SD
Location mDth (ft.).
TP-9 0-0.5
0.5-2
2+
AUGUST 1989
TEST PIT LOG
Material Fill
TOPSOIL: Light brown silty sand with abundant rootlets, dry.
BEDROCK - LINDA VISTA FORMATION:
Abundant cobbles (2-4") in red brown clayey Sand.and sandy Clay matrix.
SANDSTONE: (Linda Vista Formation) Red brown medium sandstone, dense, well cemented.
Total Depth= 2 Feet
TP-10 0-1 BEDROCK - LINDA VISTA FORMATION: Weathered sandstone.
1+ Bedrock - SANDSTONE, well cemented, near backhoe refusal.
Total Depth= 1 Foot
TP-11 0-0.5
1+
BEDROCK - LINDA VISTA FORMATION:
Weathered sandstone.
Bedrock - SANDSTONE, well cemented, near backhoe refusal.
Total Depth= 1 Foot
CeoSofIs, Inc.
APPENDIX B
GRADING GUIDELINES
GsoSoils, Inc.
GRADING GUIDELINES
Grading should be performed to at least the minimum requirements
of the governing agencies, Chapter 70 of the Uniform Building
Code and the guidelines presented below:
Site clearing
Trees, dense vegetation, and other deleterious materials should
be removed from the site. Non-organic debris or concrete may be
placed in deeper fill areas under direction of the Soil Engineer.
Light, dry grasses may be thinly scattered and incorporated into
the fill under direction of the Soils Engineer, provided
concentrations of organics are not developed.
Subdrainacre
1. Subdrainage systems should be provided in all canyon
bottoms and within buttress and stabilization fills
prior to placing fill. Subdrains should conform to
schematic diagrams GS-1, GS-3, and GS-4, approved by
the Soils Engineer.
For canyon subdrains, runs less than 500 feet may use six
inch pipe. Runs in excess of 500 feet should have the lower
end as eight inch minimum.
2. Filter material should be Class 2 permeable filter
material per California Department of Transportation
Standards tested by the Soil Engineer to verify its
suitability. A sample of the material should be
GeoSofls, Inc.
MR. PAUL SCKUPIAN W.O. 1050-SD
GRADING GUIDELINES PAGE 2
SEPTEMBER 12, 1989
provided to the Soil Engineer by the contractor at
least two working days before it is delivered to the
site. The filter should be clean with a wide range of
sizes. As an alternative to the Class 2 filter, the
material may be a 50/50 mix of pea gravel and clean
concrete sand which is well mixed, or clean gravel
wrapped in a suitable filter fabric.
3. An exact delineation of anticipated subdrain locations
may be determined at 40 scale plan review stage.
During grading,the Engineering Geologist should
evaluate the necessity of placing additional drains.
4. All subdrainage systems should be observed by the
Engineering Geologist and Soils Engineer during
construction and prior to covering with compacted fill.
5. Consideration should be given to having subdrains
located by the project surveyors. Outlets should be
located and protected.
Treatment of Existins Ground
1. All heavy vegetation, rubbish and other deleterious
materials should be disposed of off site.
CeoSofts, Znc.
MR. PAUL SCHUMAN
W.O. 1050-SD
GRADING GUIDELINES PAGE 3
SEPTEMBER 12, 1989
2. All surficial deposits of alluvium and colluvium should
be removed (see Plate GS-1) unless otherwise indicated
in the text of this report. Groundwater existing in the
alluvial areas may make excavation difficult. Deeper
removals than indicated in the text of the report may
be necessary due to saturation during winter months.
3. Subsequent to removals, the natural ground should be
processed to a depth of six inches, moistened to near
optimum moisture conditions and compacted to fill
standards.
Fill Placement
1. All site soil and bedrock may be reused for compacted
fill; however, some special processing or handling may
be required (see report).
2. Material used in the compacting process should be
evenly spread, moisture conditioned, processed, and
compacted in thin lifts not to exceed six inches in
thickness to obtain a uniformly dense layer. The fill
should be placed and compacted on a horizontal plane,
unless otherwise found acceptable by the Soil Engineer.
GeoSoCls, Inc.
MR. PAUL SCHU"
W.O. 1050-SD
GRADING GUIDELINES PAGE 4
SEPTEMBER 12, 1989
3. If the moisture content or relative density varies from
that acceptable to the Soil Engineer, the Contractor
should rework the fill until it is in accordance with
the following:
a) Moisture content of the fill should be at or above
optimum moisture. Moisture should be evenly
distributed without wet and dry pockets. Pre-watering
of cut or removal areas should be considered in
addition to watering during fill placement,
particularly in clay or dry surficial soils.
b) Each six inch layer should be compacted to at least 90
percent of the maximum density in compliance with the
testing method specified by the controlling
governmental agency. In this case, the testing method
is ASTM Test Designation D-1557-78.
4. Side-hill fills should have an equipment-width key at their
toe excavated through all surficial soil and into competent
material and tilted back into the hill (GS-2, GS-6). As the
fill is elevated, it should be benched through surficial
soil and slopewash, and into competent bedrock or other
material deemed suitable by the Soil Engineer.
GeoSoils, Inc.
MR. PAUL SC"
W.O. 1050-SD
GRADING GUIDELINES PAGE 5
SEPTEMBER 12, 1989
5. Rock fragments less than eight inches in diameter may
be utilized in the fill, provided:
a) They are not placed in concentrated pockets:
b) There is a sufficient percentage of fine-grained
c) The distribution of the rocks is supervised by the
material to surround the rocks:
Soil Engineer.
6. Rocks greater than eight inches in diameter should be
taken off site, or placed in accordance with the
recommendations of the Soil Engineer in areas
designated as suitable for rock disposal (See GS-5).
7. In clay soil large chunks or blocks are common: if in excess
of eight (8) inches minimum dimension then they are
considered as oversized. Sheepsfoot compactors or other
suitable methods should be used to break the up blocks.
8. The Contractor should be required to obtain a minimum
relative compaction of 90 percent out to the finished
slope face of fill slopes. This may be achieved by
either overbuilding the slope and cutting back to the
compacted core, or by direct compaction of the slope
face with suitable equipment.
CeoSofls, Inc.
MR. PAUL SCI"
W.0. 1050-SD
GRADING GUIDELINES PAGE 6
SEPTEMBER 12, 1989
If fill slopes are built Ifat grade" using direct compaction
methods then the slope construction should be performed so
that a constant gradient is maintained throughout
construction. Soil should not be "spilled" over the slope
face nor should slopes be "pushed outBv to obtain grades.
Compaction equipment should compact each lift along the
immediate top of slope. Slopes should be back rolled
rolled approximately every 4 feet vertically as the slope is
built.
Density tests should be taken periodically during grading on
the flat surface of the fill three to five feet horizontally
from the face of the slope.
In addition, if a method other than over building and
cutting back to the compacted core is to be employed, slope
compaction testing during construction should include
testing the outer six inches to three feet in the slope face
to determine if the required compaction is being achieved.
Finish grade testing of the slope should be performed after
construction is complete. Each day the Contractor should
receive a copy of the Soil Engineer's "Daily Field
Engineering Report" which would indicate the results of
field density tests that day.
GeoSofls, Znc.
MR. PAUL SC"
W.O. 1050-SD
GRADING GUIDELINES PAGE 7
SEPTEMBER 12, 1989
9. Fill over cut slopes should be constructed in the following
manner:
a) All surficial soils and weathered rock materials should
be removed at the cut-fill interface.
b) A key at least 1 equipment width wide and tipped at
least 1 foot into slope should be excavated into
competent materials and observed by the soils engineer
or his representative.
c) The cut portion of the slope should be constructed
prior to fill placement to evaluate if stabilization is
necessary, the contractor should be responsible for any
additional earthwork created by placing fill prior to
cut excavation.
10. Transition lots (cut and fill) and lots above stabilization
fills should be capped with a three foot thick compacted
fill blanket.
11. Cut pads should be observed by the Engineering
Geologist to evaluate the need for overexcavation and
replacement with fill. This may be necessary to reduce
water infiltration into highly fractured bedrock or
other permeable zones,and/or due to differing expansive
GeoSofls, Inc.
MR. PAUL SC"
W.O. 1050-SD
GRADING GUIDELINES PAGE 8
SEPTEMBER 12, 1989
potential of materials beneath a structure. The
overexcavation should be at least three feet. Deeper
overexcavation may be recommended in some cases.
12. Exploratory backhoe or dozer trenches still remaining
after site removal should be excavated and filled with
compacted fill if they can be located.
Gradinq Observation and Testing
1. Observation of the fill placement should be provided by
the Soil Engineer during the progress of grading.
2. In general, density tests would be made at intervals
not exceeding two feet of fill height or every 1,000
cubic yards of fill placed. This criteria will vary
depending on soil conditions and the size of the fill.
In any event, an adequate number of field density tests
should be made to evaluate if the required compaction
and moisture content is generally being obtained.
3. Density tests may be made on the surface material to
receive fill, as required by the Soil Engineer.
4. Cleanouts, processed ground to receive fill, key
excavations,subdrains and rock disposal should be
observed by the Soil Engineer prior to placing any
c GeoSoils, Inc.
MR. PAUL SC"
W.O. 1050-SD
GRADING GUIDELINES PAGE 9
SEPTEMBER 12, 1989
fill. It will be the Contractor's responsibility to
notify the Soil Engineer when such areas are ready for
observation.
5. An Engineering Geologist should observe subdrain
construction.
6. An Engineering Geologist should observe benching prior
to and during placement of fill.
Utilitv Trench Backfill
Utility trench backfill should be placed to the following
standards:
1. Ninety percent of the laboratory standard if native
material is used as backfill.
2. As an alternative, clean sand may be utilized and
flooded into place. No specific relative compaction
would be required; however, observation, probing, and
if deemed necessary, testing may be required.
3. Exterior trenches, paralleling a footing and extending
below a 1:l plane projected from the outside bottom
edge of the footing, should be compacted to 90 percent
of the
GeoSoiIs, Inc.
m. PAUL SCHUMAN
W.O. 1050-SD
SEPTEMBER 12, 1989
GRADING GUIDELINES PAGE 10
laboratory standard. Sand backfill, until it is similar to
the inplace fill, should not be allowed in these trench
backfill areas.
Density testing along with probing should be accomplished to
verify the desired results.
GeoSoits, Inc.
Final Grode _.
Mot erio /
(See Plate GS-3)
I TYPICAL TREATMENT OF
Note: Where natural slope gradient is 511 or less,
benching is not necessary unless stripping
did not remove all compressible material.
0
TYPICAL FILL OVER NATURAL SLOPE
DATE w.0.~~ 1050-SD BY GSI
Soil Mechanics Geology Foundation Engineering
I
PLATE GS-2
ALTERNATE I
SOIL - SLOPEWASH
ALLUVIUM REMOVED
TO BEDROCK
. I -’ -’. / ” /,\ BEDROCK
Canyon subdrain: 6”
perforated pipe with
9 cu. ft. grave1”per ft.
of drain.
CANYON SUBDRAIN DESIGN
AND CONSTRUCTION
DATE 9/89 W.O. NO. 1050-SD BY
Soil Mechanics Geology Foundation Engineering
ALTERNATE 2
6” perforated Pbe with
9 cu. ft. gravel * per ft. of drain
*grovel to conform to State of Calif. Dept. of Public
Works standard specifications for Class 2
permeable material.
DI ATE CC-2
~ ~~ ~
36" THICK FILL CAI?
A.
Pipe to extend
FINISHED ...
-
/ -
. .
8-
9. Buttress slope to have a bench
B. Buttress key depth varies. (see
at every 20 to 30 feet.
preliminary reports)
C. Buttress key width varies. (see
preliminary re ports )
GeoS
D. Backdrains and lateral drains
located at elevation of every
bench drain. First drain at
elevation just above lower lot
grade. Additional drains may
be required at discretion of
GeoSoils, Inc.
TYPICAL BUTTRESS SECTION
DATE .+- W.O. NO. 1050-SD BY GS1
Soil Mechanics Geology Foundation Engineering
I
xGraded filter material to conform to State of Cali!. Dept, Public Works standard specifications for.Class 2 permeoble material
-
Stack boulders end to end.
pile upon each other. Do no
ROCK DISPOSAL DETAIL
OAT E 9/89 IW.0. NQ 1050-sdBY GS1
Soil Mechanics Geology Foundation Engineering
Soil shall be pushed over rocks .and flooded into voids. Compact around and over each wind row.
' FIRM GROUND, ,- ,\ - ,\\ \\\ - \
/
/-- REMOVE ALL TOPSOIL,
COLLUVIUM AND CREEP
MATERIAL FROM TRANSITION FILL
I
I/ Typical ' , '
IO' Typical \
I
I' I I
CUT 15' Minimum
BEDROCK OR FIRM
FOR MA TI ON MATE RIAL
TYPICAL FILL OVER CUT. SLOPE
GeoS DATE 9/89 W.O. NO 1050 -SP BY-
t,. Soil Mechanics Geology Foundation Engineering