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5.3.2.3 GROSS STABILITY RESULTS <br /> As shown in Appendix E, the results of the stability analyses indicate that a static <br /> factor-of-safety of 1.5 or more can be achieved for the planned landfill geometry <br /> using a range of liner interface shear strength values (Figure 3). <br /> The pseudo-static analyses that were completed for the project to evaluate <br /> earthquake loading conditions indicate yield accelerations from about 0.10g to <br /> 0.11 g for the range of interface shear strength parameters shown in Figure 3. <br /> The yield acceleration is the seismic coefficient (k,) that yields a static factor of <br /> safety of 1.0. As shown in the calculations included in Appendix E, using these <br /> yield accelerations and the Bray & Rathje method (1998), an insignificant amount <br /> of seismic-induced permanent displacement of the landfill liner system is <br /> calculated for the two design earthquake events (i.e., Great Valley and San <br /> Andreas fault MCE's). <br /> 5.3.3 FINAL COVER SLOPE STABILITY <br /> The final cover for the proposed development is anticipated to be a multi-layer <br /> system that, from top to bottom, will consist of the following: 1-foot thick <br /> vegetative soil layer; drainage layer; 60-mil thick HDPE geomembrane, textured <br /> on both sides; 1-foot thick compacted clay layer with maximum permeability of <br /> 10-6 cm/sec and; 2- foot thick compacted foundation layer. The proposed final <br /> cover will have a slope gradient of 3:1 (H:V) between benches that will be <br /> installed on 40-foot vertical intervals. Recognizing that a drainage layer will <br /> preclude development of pore-water pressures, the interface between the <br /> vegetative soil layer and the underlying textured HDPE is considered the critical <br /> potential failure surface. <br /> 5.3.3.1 ANALYTICAL METHODS <br /> As shown in Appendix E, the semi-infinite slope analysis procedure was used to <br /> evaluate the stability of the final cover slope. Slope stability was evaluated for <br /> both static and seismic loading conditions. Since laboratory tests have not been <br /> performed to obtain shear strength parameters for the textured HDPE/vegetative <br /> soil interface, the analyses were directed to "back-calculate" the strength <br /> Forward Landfill JTD 5-16 <br /> L\Allied\2000.7 93\Reports\JTD-PCPCMP702 Sec-5.0:5/24/02 <br /> Revision 1:07/16/02 <br />