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TECHNICAL MEMORANDUM <br />Page 13 <br />June 3, 1992 <br />SAC31583.AC.ZZ <br />maximum ground surface acceleration is 0.18g for the Forward Landfill site. This ground <br />acceleration would be associated with a Richter Magnitude 7.0 MCE for the Midland fault, <br />located approximately 24 miles from. the site. A comparison of the above estimated yield <br />acceleration with the estimated maximum ground surface acceleration of 0.188 indicates that <br />permanent seismic displacement (deformation) as a result of a seismic event will be <br />negligible (i.e. less than 1 inch) (Makdisi and Seed, 1977). <br />Results of Settlement Analyses <br />Settlement of the proposed landfill extension will include both foundation settlement and <br />settlement of the refuse fill itself. This section presents the results of settlement analyses <br />and describes the analytical methods used. <br />Foundation Settlement <br />Prior to construction of the lining, a majority of the proposed landfill extension area will be <br />excavated to a depth of approximately 25 feet. The approximate limits of this proposed <br />base grading are shown in Figure 1. This subsection provides a summary of the procedure <br />used to estimate maximum foundation settlement. <br />Method of Analyses <br />Foundation settlement was estimated at the location of maximum refuse height, near the <br />center of the proposed landfill extension, at approximately the location of Boring BH -1 <br />(Figure 1). The maximum settlement at that point was estimated using conventional soil <br />mechanics theory and stress distribution techniques. <br />Settlement in the clay layers within the available depth of subsurface information (within 178 <br />feet depth) was estimated using the consolidation data presented in Appendix II. Settlement <br />within the sandy layers (sand, silty sand, clayey sand) within the available depth of subsurface <br />exploration was estimated using SPT blow -counts with the Schmertmann method (B.M. Das, <br />1984). No data is available for soil properties of foundation materials at depths in excess of <br />178 feet. Therefore, deep settlements (foundation settlements occurring at depths greater <br />than 178 feet) were estimated using an elastic theory. The elastic theory used to estimate <br />deep foundation settlements was based on an estimated average modulus of elasticity and an <br />average stress increase from the landfill extension loads. <br />11 <br />