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eh <br />ESPEY, HUSTON & ASSOCIATES, INC. <br />• <br />Geometry Factor of Safety <br />Phase I Refuse Fill -critical circulaz failure surface 2.5 <br />Final Refuse Fill -critical circular failure surface 1.5 <br />Final Refuse Fill -trial wedge failure surface 1.6 <br />The critical circulaz failure surface for the Phase I Refuse Fill passed <br />through both Material I and Material II and indicates a toe failure of the slope. The <br />critical circulaz failure surface for the Final Refuse Fill is entirely contained within <br />Material I, and is tangent to the interface between Material I and Material II. Since <br />the assumed water level after construction of the fill is located below this <br />interface, vaziation of the water level from assumed conditions will not affect the <br />results of the Final Refuse Section stability analysis unless the actual potentio- <br />metric surface elevation is within Material I. <br />• Because of the relatively high factor of safety (2.5) associated with the <br />Phase I Refuse Fill Section as analyzed, significant variations in water level from <br />assumed conditions aze not expected to reduce the factor of safety below minimum <br />standards. <br />A pseudo-static analysis has been accomplished by others for a similaz <br />final refuse fill geometry, yielding a minimum factor of safety of 1.3 for a geometry <br />that had a static factor of safety of 1.5. This pseudo-static analysis incorporated a <br />horizontal force of 0.025g to simulate the effect of an earthquake on the stability of <br />the slope. The results of this analysis aze assumed to be applicable to the final <br />refuse fill geometry analyzed by EH&A, based on similarities of overall slope <br />gradients and static factors of safety. <br />The field investigation conducted by EH&A included standard penetra- <br />tion tests on in situ materials. These tests did not indicate the presence of loose <br />sands in the existing soil. The possibility of liquefaction of foundation materials <br />during an eazthquake is therefore minimal. The use of more sophisticated dynamic <br />analysis methods is thus not considered to be wazranted. <br />13-9 <br />