607 RIVERSIDE RD Geotech Report 2022-10-25

I March 22,2016 IProject No.T-7388 Based on the soil conditions encountered and the local geology, the 2012 International Building Code (IBC) Iindicates that site class"D"should be used in structural design. ISeismic Design Parameters(IBC 2012) Spectral response acceleration(Short Period), SMs 1.241 I Spectral response acceleration(1 Second Period), SM, 0.720 Five percent damped 0.2-second period, Sips 0.827 Five percent damped 1-second period, SDI 0.480 The above values are for Latitude 48.00842N and Longitude -122.18405W, and were obtained from United 111 States Geologic Service(USGS)Ground Motion Parameter Calculator(accessed March 16,2016). I5.0 DISCUSSION AND RECOMMENDATIONS I5.1 General Based on our study, in our opinion, development of the site as proposed is feasible from a geotechnical engineering standpoint. The primary geotechnical concern at the site is the presence of compressible soil strata susceptible to consolidation under the planned building loads. The compressible soil consists of a 10-to 12-foot thick layer of very soft to soft organic silt and clay underlying the site's upper fills. Laboratory testing indicates Ithe very soft organic silt and clay are highly compressible and if not mitigated,unacceptable levels of differential building:settlement would likely occur under proposed project loads. Given the depth to the very soft soil layer, in our opinion, the potential post construction building settlements can be mitigated by implementing a fill Isurcharge program. The existing fills at the site consist mostly of silty sand soils with varying amounts of gravel and minor amounts Iof organics. Observations noted the fill to be in a medium dense condition in most site areas and, in its current condition, appeared suitable for support of new fill,pavements,or building elements. Some areas showed the fill to be in a loose condition, which will require removal to a minimum depth of two feet below base-of-footing Ielevation and replacing with compacted structural fill. The need for overexcavation will require confirmation by geotechnical observation and testing at the time of grading as outlined in the following Site Preparation and I Grading Section. The existing fill and underlying native soils are moisture sensitive and close moisture control will be required to facilitate structural compaction of the soils if used as fill from site excavations. I Detailed recommendations regarding these,issues and other geotechnical design considerations are provided in the following sections. These recommendations should be incorporated into the final design drawings and construction specifications. I Page No.4 I