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(ii) weathered rock, overburden, up to 15 m high - 1(V) : 2.5(H) <br />(iii) weathered rock, overburden, greater than 15 m high - 1(V) : 3(H) <br />(Geotechnical Slope Stability, January, 1995.) <br />Waste rock pile will be graded at 3(H):1(V), or 18.43° (case ii) putting the waste pile well <br />within the recommended range. <br />Foundation Stability <br />The foundation of the waste rock pile is a flat, well compacted surface. The underlying <br />soils have high clay content and there are no known aquifers under the pile. Therefore, <br />there is no water that could enter the pile from below and compromise the stability of the <br />underlying soils or the waste rock pile itself. <br />Factor of Safety (FS) <br />For infinite slopes consisting of cohesionless soils that are either above the water table or <br />are fully submerged, the factor of safety for slope stability is determined as follows: <br />FS = Tancp/Tan13 where <br />cp = the angle of internal friction for the soil <br />13 = the slope angle relative to the horizontal <br />(WSDOT Geotechnical Design Manual M) <br />There could be a small amount of cohesion which would add to the strength but this will <br />be ignored in order to calculate the worst case scenario. <br />FS = tan (40 °) /tan (18.43 °) = 2.518 <br />> 1.4 is the recommended parameter for safety factor of permanent slopes. <br />Thus the 3:1 slope satisfies the Factor of Safety for this material. <br />