specs

Geotechnical Investigation South River Place, Gasser Drive, Napa 29 December 2010
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Foundations
Based on our field and laboratory investigation, the subsurface soils have the potential for
settlement due to seismically induced liquefaction and consolidation of the subsurface soils as
identified above. As stated above, the liquefaction and consolidation hazards must be mitigated by
over-excavation and recompaction of the old fill soils or by in-situ densification. In addition, the
site’s near surface foundation soils are considered to have a low to high expansion potential and
susceptible to potential differential movements due to variations in moisture content. Therefore,
provided the building pads are graded as recommended above, the buildings may be satisfactorily
supported on a deepened, interconnected spread footing foundation system in conjunction with
interior slabs-on-grade. Recommendations for the spread footing foundation system where
densification by conventional grading techniques is performed are presented below. If in-place
densification is performed, the foundation criteria should be provided by the densification designer.
Spread footings should extend to a minimum depth of 30 inches below lowest adjacent pad grade
(i.e., trenching depth). At this depth, the recommended design bearing pressure should not
exceed 2,000 p.s.f. due to dead plus sustained live loads. The above allowable pressure may be
increased by 1/3 due to all loads which include wind and seismic. Isolated footings are not
recommended. All footings must be interconnected with continuous footings or tie-beams. All
foundations must be adequately reinforced to provide structural continuity and resist the
anticipated loads as determined by the project Structural Engineer. However, continuous
footings are to be reinforced with a minimum of 4 No. 5 bars, 2 at the top and 2 near the bottom
of the footing. Additional reinforcement will be as required by the structural engineer and in
accordance with structural building code requirements. Foundations designed in accordance
with the above criteria should be expected to experience a total settlement of 1 inch and a
differential of ½ inch.
To accommodate lateral building loads, the passive resistance of the foundation soil can be
utilized. The passive soil pressures can be assumed to act against the front face of the footing
below a depth of 1 foot below the ground surface. It is recommended that a passive pressure
equivalent to that of a fluid weighing 250 p.c.f. be used. For design purposes, an allowable
friction coefficient of 0.30 can be assumed at the base of the spread footings.
Two bag samples of the near surface soils on Retail 1 and 2 pads were collected and transported
to Sunland Analytical in Rancho Cordova for testing of water soluble sulfates in accordance with
California Test Method 417. The testing indicates a sulfate content ranging from 32.3 to 124.0
ppm (mg/kg) for the samples collected. Based on exposure conditions as identified in Table 19-
A-4 of the California Building Code, the building site is classified as “Negligible” which
requires no special provisions for cement type, concrete strength, or water/cement ratio.
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KC ENGINEERING COMPANY Project No. VV3200 Page 20 of 123