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GEOTECHNICAL STABILITY EXHIBIT <br /> There are no buildings or any structures outside the permit area which could be affected by the <br /> excavation. Sufficient buffers will be maintained to neighboring property lines. <br /> From Table 2.5 in the SME Mining Reference Handbook', the backfill is best classified as sand <br /> and gravel, mixed grain size. This material has an internal angle of friction of approximately 48 <br /> degrees and no cohesion. <br /> The Factor of Safety (FOS) for sand and gravel with a(3H:IV) 18.4 degree slope in sand and <br /> gravel material with an assumed internal angle of friction of 48 degrees can be approximated by <br /> evaluating the internal angle of friction as follows: <br /> FOS = Tangent of Internal Angle of Friction <br /> Tangent of Actual Angle of Failure Surface <br /> Tan 48' 1.200 <br /> FOS = — = 3.61 <br /> Tan 18.4° 0.3326 <br /> With a safety factor of 3.61, 3H:1 V slopes will be safe as the final condition. <br /> • o0 <br /> Ben Langenfeld, P.E. <br /> _. 0047151 m; <br /> a. P.E.# 0047151 <br /> ".1��Pf.a•amaoa••aC°�Cy\`w• <br /> Date. lZ <br /> Original source: Houk and Bray 1977 <br /> Robinson Gravel No 1 <br /> September 2018 GS-1 <br />