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amec z <br /> foster <br /> wheeler <br /> levels occur mainly during the winter and early spring months verses lower levels during the dry <br /> weather period of summer and early fall. Throughout the year, groundwater levels would likely <br /> fluctuate in response to changing precipitation patterns, construction activities, and site utilization. <br /> 3.4 SEISMIC CONDITIONS <br /> The soils underlying the few feet of fill consist of soft to very stiff sandy silt or silt (Recessional <br /> Lacustrine). We interpret the soils beneath the site to be Site Class D, as defined in the International <br /> Building Code (IBC). <br /> Liquefaction Evaluation: As mentioned, the soils underlying the site consist of lacustrine silt. No <br /> groundwater was encountered in these soils. Based on the fine-grained soil, rather than sands, and <br /> the assumption that groundwater is deep, it appears that the risk of soil liquefaction at this site is very <br /> low. <br /> Seismic Design Parameters: The IBC requires use of Risk-Targeted Maximum Considered <br /> Earthquake (MCER) Ground Motion Response Acceleration for design of structures. Based on <br /> detailed U.S. Geological Survey hazard mapping for this site, we recommend the following <br /> parameters for structural design, for the design earthquake having a 2 percent probability of <br /> occurrence in 50 years (return interval of 2,475 years): <br /> Use IBC Soil Class D with: <br /> ► SS = 1.30g <br /> ► S1 = 0.496g <br /> ► SDS = 0.870 g <br /> ► So1 = 0.497g <br /> Where g is the acceleration due to gravity. <br /> 4.0 CONCLUSIONS AND RECOMMENDATIONS <br /> This section presents our geotechnical engineering conclusions and recommendations concerning <br /> site preparation, foundations, floors, drainage systems, backfilled walls, utilities, stormwater <br /> infiltration, pavement, and structural fill. ASTM International (ASTM) specification codes cited herein <br /> 111 refer to the most current applicable ASTM manual. Washington State Department of Transportation <br /> (WSDOT) specification codes cited herein refer to the current WSDOT publication M41-10. <br /> Amec Foster Wheeler <br /> Project No.6-917-18116-0 7 <br /> \\Sea-fs1\WordProc\ Projects\18000s\18116 Everett School District\Geotech Report\Revised\2017_10-19_Everett Middle School Geotech_Sx.docx <br />