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U <br />CONCLUSIONS A:/ RECOMMENDATIONS <br />This section presents conclusions and recommendations based on the static and seismic <br />slope stability analyses presented in this report for Module 1 of the FSL site. <br />5.1 Conclusions <br />5.1.1 Stability of Liner System <br />The sideslope liner will be installed on slopes of up to 3H:1 V. An infinite slope stability <br />analysis shows that the interface/internal shear strength with sideslope liner system <br />should meet a minimum friction angle of 22.6 degrees over a normal stress range of 0 to <br />500 psf. It is concluded that with the use of a HDPE geomembrane textured on both <br />sides, and with the use of a shear -reinforced GCL, the required shear strength is <br />achievable because of the low normal stress level involved. <br />Perched water conditions can impact the integrity of the installed liner system on the side <br />slopes before waste is placed against it. The potential for perched water conditions <br />should be assessed during construction and appropriate remedial measures should be <br />taken to prevent uplift pressure on the liner system. <br />5.1.2 Global Slope Stability — Static Conditions <br />The results of static slope stability on the three critical cross-sections show that both the <br />base and sideslope liner systems should meet a minimum residual internal/interface shear <br />strength envelope defined by a friction angle of 10.5 degrees over a normal stress range <br />of 0 to 12,000 psf. The waste sideslopes should not exceed 3.5H:1 V along the southern <br />and eastern perimeters of Module 1. The western slope can have a sideslope of 3H: IV. <br />Also, 20 -foot wide benches at elevations 300, 350, and 400 feet should be provided on all <br />three slopes. <br />5.1.3 Global Slope Stability - Seismic Conditions <br />The pseudo -static slope stability analysis on all three cross-sections performed using the <br />shear strength and waste slope requirements determined from the static analysis noted <br />above yielded an identical yield acceleration of 0.09g. The yield acceleration is <br />significantly higher than the peak horizontal ground acceleration of 0.054g. <br />\\SACRFPI\COMMOMsacDP\2002\PRJ\PJ8\83\835608.2bz.doc EMCONIOWT, Inc. <br />\ Rev. 0, 07/31/02 <br />5-1 <br />