4027 4TH ST SE 2018-01-01 MF Import

January (4,2003 HWA Proiect No. 2002-146-21 3.3.2 Ground water Ground water levels could not be observed in the borings due to the use of drilling tluid; however, we anricipate that ground water levels will fluctuate, primatily in response to changes the level of the river. For design purposes and based on the mnisture content of the soil samples, the ground water was estimated at 8 feet below ground surface (El. 2 ft). 4.0 CONCLUSIONS AND RECOMMENDATIONS 4.1 GENERAL 1'he main geotechnical issue affecting design is the presence of two soft silt and clay layers (an upper layer 15 feet thick and a lower layer 45 feet thick) within the soil profile. The combined presence of soft silt/c(ay and potentially liquefiable sands and silty sands within the upper portion of the soil profile, necessitate the use of deep foundations. The presence �f the two layers of compressible soil results in relatively high settlements anticipated for fills, pile caps and the piles, which must be considered in design. The design options to deal with the large amounts of settlement and the potentially liquefiable soils aze to either drive the piles into the glacially consolidated deposits beyond elevation —87 feet, or drive the piles to bear in the non-liquefinble, medium drnse sand layer. If the piles are "hung-up" in the medium dense sand layet, some settlement of the building will occur due to consolidadon of the soil in the lower soft layer and some settlement could occur during an earthquake. Based on our understanding that previous pile foundations have been founded in the sand and have reportedly perfoRned well, we believe founding the piles at elevation —35 will provide a foundation which will perform consistent with the other buildings at the site. Tab(e 1 prese��ts a summary of the design recommendations presented in the following sections. Table 1: Recommended Design Parameters 2002146 re{ron - �nal 6 HWA GEOSCIENCES INC. U