HomeMy WebLinkAboutOC_RS071757 - Soils3.2 Soil Conditions
The borings encountered fill which was placed during the tract rough grading. The fill was
found to consist predominantly of silty clay with lesser rock fragments and sand content at
some intervals.
The fill was found to be generally well compacted and consistent in both borings and at
varying depths within each boring. Our review of the GMU rough grading report (2004) in-
dicates that between 143 and 186 feet of fill was placed below the subject lot.
Ground water was not encountered in our borings and is not considered a significant factor
in the development.
No evidence of shallow or perched ground water has been noted in the form of seeps,
springs, tufa deposits, mineral efflorescence, or concentrated growth of phreatophyte plants
was encountered during this investigation.
More detailed descriptions of the subsurface conditions are shown on the attached boring
logs.
3.3 Seismicity
The subject property is not located within any Alquist-Priolo Special Studies Zones or
astride a known, active or potentially active fault, and, accordingly, need not be considered
for potential surface fault rupture.
As the site is located in southern California, however, it is subject to strong ground shaking
by a nearby or distant strong earthquake. However, the performance of structural engineer
designed structures, built in compliance with current building codes and founded into prop-
erly prepared earth materials, has generally proven to be satisfactory under conditions of
earthquake induced strong ground shaking away from "near -field" fault rupture areas.
Earthquakes which might occur on faults within a 60 mile (100 km.) radius from the site are
listed below on Appendix Pages "seis-1-9" of this report, along with their seismic parame-
ters.
Secondary seismic hazards that are also considered for this project are liquefaction, seismic
settlement, differential compaction, landsliding, earthquake induced flooding, tsunamis, and
seiches. Each is addressed below.
Potential for liquefaction, seismic settlement and differential compaction - is consid-
ered very low to negligible based on the lack of ground water, the clayey and compact
nature of the fill beneath the site, and replacement of readily compressible surficial
soils with engineered fill.
Potential for landsliding - is considered to be low, based on our review of the refer-
enced GMU report, the clayey nature of the fill slope soils, and the generally excellent
appearance of the slopes which were completed several years ago.
Potential for earthquake induced flooding, tsunamis, and seiches - can be precluded,
as no upstream dams or other nearby bodies of water are present.
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5.1.4 Soil Design Parameters (Section 1815, 1997 UBC)
The following geotechnical design parameters are presented, as defined in UBC Section
1815.2, Symbols and Notations:
Parameter Design Value
Co 1.8
C. 1.0
C, 15
PI 28
q„ 100 psf
Effective PI=C.xC.x PI= 1.8x1.0x28= 50
5.1.5 Seismic Design
Seismic design of the structures should be performed using criteria presented in the Uniform
Building Code (UBC) for Zone 4 seismic conditions.
Seismic design parameters required by the 1997 UBC and the State of California Seismic
Hazards Act are included on Appendix Pages "leis -1-9" of this report. Recommended de-
sign parameters are as follows:
Design Parameter Recommended Value
Design Fault Newport -Inglewood
Fault/Site Distance 4.3 km
Maximum Site Acceleration
0.46g
Soil Profile Type
So
Na
1.1
N„
1.3
Ca
0.47
C„
0.83
Ts
0.702
To
0.140
5.2 Retaining Walls
Retaining walls may be designed using the following parameters:
Bearing - See Soil Bearing Section above
Active Earth Pressure (Cantilevered Walls)
Level Backfill - 32 psf/ft
At -Rest Earth Pressure (Restrained At Top Walls)
Level Backfill - 50 psf/ft
Passive Earth Pressure - 295 psf/ft (ignore Upper 1 foot)
Sliding Coefficient - 0.40
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