HomeMy WebLinkAboutCDP 96-14; Marja Acres PCS Facility; Coastal Development Permit (CDP) (12)HETHERINGTON ENGINEERING, INC.
SOIL & FOUNDATION ENGINEERING • ENGINEERING GEOLOGY • HYDROGEOLOGY
May 14, 1996
Project No. 1519.1
Log No. 2265
J. M. Consulting Group
3530 Camino Del Rio North, Suite 101
San Diego, CA 92108
/
Attention: Ms. Cheryl M. Hacke
Subject: SUPPLEMENTAL GEOTECHNICAL INVESTIGATION
Proposed Cox California PCS Station
SD154-Marja Acres
Carlsbad, California
Reference: "Geotechnical Investigation, Proposed Cox
California PCS Station, SD154-Marja Acres,
Carlsbad, California," by Hetherington Engineering,
Inc., dated February 21, 1996.
Dear Ms. Hacke:
In accordance with the request of Ms. Blanca Bracamontes of your
office, we have performed a supplemental geotechnical investigation
at the subject site. The purpose of our additional investigation
was to evaluate soil and geologic conditions, and provide grading
and foundation recommendations for the proposed revised location of
the equipment storage area. To assist with our investigation, we
were provided with a Site Plan, prepared by Gold Coast Surveying.
With the above in mind, our supplemental work included the
following:
o Subsurface exploration consisting of one backhoe trench to
obtain soil and bedrock samples and observe geologic
conditions.
o Laboratory testing.
o Engineering and geologic analyses.
o Preparation of this report providing the results of our field
and laboratory work, analyses, and our conclusions and
recommendations.
SITE DESCRIPTION AND PROPOSED DEVELOPMENT
It is our understanding that the revised location for the equipment
storage area is within the toe area of the existing slope
immediately south of the asphalt concrete driveway/parking area and
Country Store building. The equipment storage area will reportedly
5245 Avenida Encinas, Suite G • Carlsbad, CA 92008-4369 • (619) 931-1917 • Fax (619) 931-0545
32242 Paseo Adelanto, Suite C • San Juan Capistrano, CA 92675-3610 • (714) 487-9060 • Fax (714) 487-9116
SUPPLEMENTAL GEOTECHNICAL INVESTIGATION
Project No. 1519.1
Log No. 2265
May 14, 1996
Page 2
consist of an approximate 10 feet by 20 feet pad excavated into the
north facing hillside and bounded by retaining walls up to 10 feet
high (maximum) . We understand that the two antenna sites have been
relocated approximately 10 feet downslope from their original
proposed locations.
SUBSURFACE EXPLORATION
Subsurface conditions were explored by excavating one backhoe
trench into the hillside, to a depth of approximately 10 feet
measured at the south wall of the trench. The approximate location
of the trench is shown on the attached Plot Plan, Figure 1.
The subsurface exploration was supervised by a geologist from this
office, who visually classified the soil and bedrock materials, and
obtained bulk and undisturbed samples for laboratory testing. The
soils were visually classified according to the Unified Soil
Classification System. Classifications are shown on the Trench
Log, Figure 2.
LABORATORY TESTING
Laboratory testing was performed on samples obtained during the
subsurface exploration. Tests performed consisted of the
following:
o Dry Density and Moisture Content
(ASTM: D 2216)
o Maximum Dry Density/Optimum Moisture Content
(ASTM: D 1557-91A)
o Direct Shear
(ASTM: D 3080)
Results of the dry density and moisture content determinations are
presented on the Trench Log, Figure 2. The remaining laboratory
tests are presented on Figure 3.
SOIL AND GEOLOGIC CONDITIONS
Soil and geologic conditions encountered in this phase of
subsurface work are similar to those described in our previous
report (Reference 1) . The proposed construction site for the
equipment storage area is underlain by surficial soils consisting
of colluvium, which is in turn underlain by Santiago Formation
bedrock. The colluvium ranges from approximately 5 feet thick on
HETHERINGTON ENGINEERING, INC.
SUPPLEMENTAL GEOTECHNICAL INVESTIGATION
Project No. 1519.1
Log No. 2265
May 14, 1996
Page 3
the south wall of the trench to approximately 3 feet thick near the
toe of the slope and consists generally of very moist, soft to
stiff, dark brown to dark olive brown fine sandy clay. Bedrock
materials encountered in the trench consist of moist, dense to very
dense, moderately cemented, light green to light gray silty fine
sandstone. No groundwater was observed in the exploratory trench.
CONCLUSIONS AND RECOMMENDATIONS
1. General
The proposed relocation of the equipment storage area is
feasible from a geotechnical standpoint. Grading and
foundation plans should take into account the appropriate
geotechnical features of the site.
2. Site Grading
Following excavation into the north facing hillside to create
the relatively level pad for the equipment storage area, any
exposed colluvium should be removed down to bedrock and
replaced as compacted fill. Fill should consist of sandy
soils derived from the underlying bedrock.
Fill should be compacted by mechanical means in uniform
horizontal lifts of 6 to 8-inches in thickness. All fill
should be compacted to a minimum relative compaction of 90
percent based upon ASTM: D 1557-91A. Soils used as compacted
fill should be placed at about optimum moisture content. Rock
fragments over 6-inches in dimension and other perishable or
unsuitable materials should be excluded from the fill. All
grading and compaction should be observed and tested as
necessary by the Geotechnical Engineer.
3. Foundation and Slab Recommendations
a. The proposed equipment storage area may be supported on
conventional continuous footings bearing entirely in
bedrock. Footings should extend to a minimum depth of
12-inches into bedrock. Footings located adjacent to
utility trenches should extend below a 1:1 plane
projected upward from the inside bottom corner of the
trench. Continuous footings should be reinforced with a
minimum of two #4 bars, one top and one bottom.
Footings bearing as recommended may be designed for a
dead plus live load bearing value of 2000 pounds per
HETHERIIMGTON ENGINEERING, INC.
SUPPLEMENTAL GEOTECHNICAL INVESTIGATION
Project No. 1519.1
Log No. 2265
May 14, 1996
Page 4
square foot. This value may be increased by one-third
for loads including wind or seismic forces. A lateral
bearing value of 200 pounds per square foot per foot of
depth and a coefficient of friction between foundation
soil and concrete of 0.4 may be assumed. These values
assume that footings will be poured neat against the
foundation soils. Footing excavations should be observed
by the Geotechnical Engineer prior to the placement of
steel to ensure that they are founded in suitable bearing
materials.
Floor slabs should have a minimum thickness of 6-inches
and should be reinforced with at least #4 bars spaced at
12-inches, center to center, in two directions, and
supported on chairs so that the reinforcement is at mid-
height in the slab. Prior to placing concrete, the slab
subgrade soils should be thoroughly moistened.
b. Antennas
The antennas located on the slope should be designed in
accordance with our previous recommendations contained in
the referenced report.
4. Retaining Walls
Retaining walls free to rotate (cantilevered walls) should be
designed for an active pressure of 40 pounds per cubic foot,
equivalent fluid pressure, assuming level backfill consisting
of on-site soils derived from the bedrock material or imported
granular material. Walls restrained from movement at the top
should be designed for an additional uniform soils pressure of
8xH pounds per square foot where H is the height of the wall
in feet. Any additional surcharge pressures behind the wall
should be added to these values. Retaining wall footings
should be designed in accordance with the previous building
foundation recommendations. Retaining walls should be
provided with adequate drainage to prevent buildup of
hydrostatic pressure and should be adequately waterproofed.
Temporary construction slopes necessary to facilitate wall
installation should be inclined no steeper than 1:1
(horizontal to vertical) and observed by the geotechnical
consultant to assure conditions are as anticipated.
HETHERINGTON ENGINEERING, INC.
SUPPLEMENTAL GEOTECHNICAL INVESTIGATION
Project No. 1519.1
Log No. 2265
May 14, 1996
Page 5
5. Trench and Retaining Wall Backfill
All trench and retaining wall backfill should be compacted to
at least 90 percent relative compaction and tested by the
Geotechnical Engineer.
6. Grading and Foundation Plan Review
Final grading and foundation plans should be reviewed by the
Geotechnical Consultant to confirm conformance with the
recommendations presented herein or to modify the
recommendations as necessary.
LIMITATIONS
The analyses, conclusions and recommendations contained in this
report are based on site conditions as they existed at the time of
our investigation and further assume the excavations to be
representative of the subsurface conditions throughout the site.
If different subsurface conditions from those encountered during
our exploration are observed or appear to be present in
excavations, the Geotechnical Engineer should be promptly notified
for review and reconsideration of recommendations.
This opportunity to be of service is appreciated. If you have any
questions, please call Danny Cohen at the Carlsbad office.
Sincerely,
HETHERING
DANNY COHEN
Civil Engin
(expires 3Geotechnical
(expire 3/31/00
BRANDON A. BOKA
Senior Engineering
Registered Geologist 5913
Certified Engineering Geolog
(expires 3/31/98)
MDH;DC;BAB/sl
HETHERINGTON ENGINEERING, INC.
(E) BUILDING
ROOF RIDGE LINE 73.4'
ASPHALT HAVEMENT
PROPOSED ANTENNA
ARRAY
PROPOSED EASEXOT
U.G. CABLE
LEGEND
APPROXIMATE SCALE: 1'=40'
T-1
APPROXIMATE LOCATION OF
BACKHOE TRENCH
PLOT PLAN
HETHERINGTON ENGINEERING, INC.
GEOTECHNICAL CONSULTANTS
JMCG/COX-SO 154
Marja Acres. Carlsbad
PROJECT NO. 1519.1 FIGURE NO. 1
om EARTH MATERIALS
COLLUVIUM: Dark brown to dark olive brown fine sandy clay, very moist, soft,
rootlets, some random 1/32" caliche veins.
@18": Becomes firm to stiff, some 1/32" caliche veins, some 1/2"
diameter inclusions of white sandstone, trace rootlets
@ 5': Contact dips about 32 to 22 degrees north
BEDROCK; Light green to light gray silty fine sandstone, moist, dense to very
(Santiago dense, moderately cemented.
Formation) @ 5' to 6': weathered, fractured, dense, abundant caliche along
fractures, rootlets.
@ 7': Decrease in caliche and fracturing, becomes very dense.
ATTITUDES
6': Caliche lined
iractures, N70E/86SE,
:uts laminae @ 7 1/2'
7 1/2': Approximate
L/8 to 1/4' caliche
.aminae in approximate
i" wide orange stained
'.s., undulatory, fairly
Continuous, N55E/09NW
O
5'
DryDensity
(pcf)
98
104
138
Chn>
Moisture
Content
19,2
19.9
7.3
Sample Depth
X
GRAPHIC REPRESENTATION SCALE- r-s- (HV)
SANTIAGO FOFIMATION
ASPHALT PAJVEMENT
4r
n
|—
O(Q(D
CDQ.
CD><BH
DOm
E P z
O
T
CDD
21o"
3
m
P m
r~OOo$ z
SUMMARY OP MAXIMUM DRY DENSITY/OPTIMUM MOISTURE CONTENT DETERMINATIONS
(ASTM: D 1557-91A)
Sample
Location
Description Maximum
Dry
Density
(pcf)
Optimum
Moisture
Content
TP-1 @ 5'Light gray silty fine sand 113.0 15.0
DIRECT SHEAR
(ASTM: D 3080)
Sample Location
TP-1 @ 5'
Cohesion
(psf)
225
Internal Angle of
friction ( • )
30
Remarks
Remolded to 90% of
maximum, consolidated,
saturated, drained
Project No. 1519,
Figure No.