Laserfiche WebLink
June 9,2022 <br /> Page 7of15 <br /> Geotechnical Evaluation <br /> Seismic Design Parameters(ASCE 7-16) <br /> Site Spectral Spectral Site Design Spectral Design <br /> Class Acceleration Acceleration Coefficients Response Parameters PGA <br /> at 0.2 sec.(g) at 1.0 sec.(g) <br /> Fa Fv SDS SDI. <br /> D 1.345 0.477 i.o Null 0.897 Null 0.58 <br /> Additional seismic considerations include liquefaction potential and amplification of ground <br /> motions by soft/loose soil deposits. The liquefaction potential is highest for loose sand with a <br /> high groundwater table. The site has a low likelihood of liquefaction. For items listed as "Null" <br /> see Section 11.4.8 of the ASCE. <br /> Conclusions and Recommendations <br /> General <br /> The site area is underlain by areas of fill and at depth by outwash sands. New foundation <br /> elements may bear on medium dense or firmer native soils. Any fill and loose soils should be <br /> removed from below foundation elements and replaced with concrete or crushed rock. Local <br /> overexcavation work could be required. <br /> We recommend a minimum 7 feet effective setback for foundation elements closest to the steep <br /> slopes (or within the steep slopes). The effective setback is the horizontal distance from the <br /> closest footing edges to the adjacent slope face. In addition to this setback, we recommend that <br /> foundation elements closest to the east property line be embedded to a depth to create a <br /> minimum 1H:1V envelope from the base of the footing to the toe of the slope. This should be <br /> provided in pictorial form on the architectural plans for review. Note that the 7 foot effective <br /> setback may end up being greater due to the 1H:1V requirement. <br /> This will likely require deepening the easternmost footing elements several feet. No buffer is <br /> warranted since the areas have been previously graded and should be re-graded to a more stable <br /> configuration. <br /> It is feasible to modify the already modified east slopes to create a more stable configuration. <br /> Steep slopes should be re-graded to a maximum 2H:1V magnitude in native soils and re- <br /> vegetated. Alternatively, one or more retaining walls could be constructed near the east property <br /> line to increase stability. <br /> Infiltration is generally feasible in the outwash sands that underlie the site. Since the site <br /> contains steep slopes and the proposed construction includes a basement level, specific <br /> recommendations regarding system depths and locations must be followed.We must be provided <br /> with the final civil plans for review and we should be on site during construction to verify soil <br /> conditions, elevations, and locations of the new systems. We can provide additional <br /> recommendations once a civil plan has been prepared. <br /> www.cobaltgeo.com (206)331-1097 <br />