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For the purpose of a conservative geotechnical analysis of the backfill's slope stability, cohesion <br /> will be ignored. Therefore,the slope stability can be evaluated by comparing the slope angle to <br /> the internal angle of friction of the material. For GC material this is 31° or greater. <br /> Safety Factor = tangent of internal angle of friction <br /> tangent of the actual slope <br /> Safety Factor = tan(310) <br /> tan(18.4°) <br /> Safety Factor = 1.81 <br /> The backfilled slope is located significant distance from the ground water table, and any <br /> structures that may be damaged by a slope failure. Additionally, the backfill material in question <br /> has been shown to be stable in stockpiles with slopes of 1.8H:1 V for years at a time. Therefore, <br /> the minimum Safety Factor for the backfill slope is 1.3. The analysis above shows that the slope <br /> has a Safety Factor of 1.8, well in excess of the minimum. The backfill slope, as designed, is <br /> safe. <br /> The north property backfill will be installed in lifts of no more than 18 inches in thickness,to a <br /> compaction standard of 90%of maximum dry density. This compaction standard is easily <br /> achieved by dozer and other equipment driving across the lifts following placement. Compaction <br /> will be checked a minimum of once per lift. <br /> u _f <br /> �;s <br /> �:'�� <br /> •-,y "sf��ea8 <br /> Ralston Quarry e:"g 1. idu and Associates,PLLC <br /> January 2019 GS-4 <br />