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Subsurface Fxploration, Geologic Nazard, and <br />Rrl��edcre Lots Erut Prefimiwry Georechnirnl Engineering Report <br />Evrretr 11'ashington Geolagic Nazards and Mirigations <br />e��atuation o( a rotational failure. Input parameter� for the analysis included slope geome[ry, <br />geology and ground water conditions, soil strength parameters, and seismic conditions. For <br />evaluation of slope stability under seismic conditions, a horizontal ground acceleration of 0.2g <br />was used in our analysis. This corresponds to an approximate 1-in-100-year seismic event. <br />The slope geometry was develoPed from the topography depicted un the topographic site plan <br />prepared by ASPI. Soil strength parameters were estimated based on laboratory direct sheaz <br />and bulk densiry testing of selected samples, pu6!ished data, and our experience with similar <br />sediments encountered in the Puket Sound region. Soil strength parameters used in our <br />anal��sis for each of the geologic units encountered are summarized below in Table l. <br />Tablc 1 <br />Summary of Soil Strcngth Parameters <br />�" pcf = pounds per square foo�. <br />''' pc( = pounds �nr cuhic fooi. <br />,A slope profile through line A-A' ����s evaluated (or our analysis (Figure 2). Although Profile <br />A-A' is modeled after slope conditions on Lot 33, similar topographic and geologic ecnditions <br />Here encountered on Lots 32 and 3�i. <br />The stabiliry of a slope can be expresscd in terms of its factor of safery. The factor of safery ;' <br />the ratio betH�een the forces that resist sliding to the forces that drive sliding. For example, a <br />factor of safety of 1.0 would indicate a slope where the driving forces and the resisting forces <br />are exactly equal. Increasing factor of safety values greater than 1.0 indicate increased <br />stabilin�. Factors of safery below 1.0 indicate conditions where driving forces exceed resisting <br />forces and landsliding is imminent. As a general standard of practice, factors of safery of 1.5 <br />and 1.1 are considered to be the minimum acceptable values for slope stability under s[atic and <br />seismic conditions, respectively. Copies of the slope profiles showing calculated factors of <br />safety for static and seismic rnnditions and the associated theoretical failure surfaces are <br />included in �he ,4ppendix. <br />`��—�� �i s, ,iK��� ASSOGATED E,1RTH SCfENCES, lNC. <br />������. ,.�,���,�,�. ��,,,,.���z��„�,����:c��k�r� N_�. Page7 <br />