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To DRMS Den Page 5 of 5 2017-07-12 22.12 51 (GMT) 13032008630 From Greg LewcKj <br /> Geotechnical Stability Exhibit <br /> The permanent slopes in place at the Flayden Gravel Pit will be 3H:IV or shallower as shown on <br /> Map F of the approved permit. <br /> From Table 2.5 in the SME Mining Reference liandbookl,the backfill is best classified as loose <br /> sand,mixed grain size;.This material has an internal ankle of friction of approximately 34 degrees <br /> and no cohesion. <br /> The Factor of Safety(FOS)for sand and gravel with a(3H:1 V) 18.4 degree slope in loose sand <br /> material with an assumed internal ankle of friction of 34 degrees can be approximated by <br /> ignoring the cohesion component of the stability and simply evaluating the internal angle of <br /> friction as follows: <br /> FOS= Tan ent of Internal Angle of Friction RECEIVED <br /> Tangent of Actual Angle of Failure Surface UL 13 201 <br /> J <br /> ;�ec�arn <br /> FOS= _ Tau 340 _ 0.6745 _ 2.0� &Safety <br /> Tan 18.40 0.3326 <br /> The permanent slopes at the White;River City Pit will be stable,and not risk any neighboring <br /> structures. <br /> E • <br /> a V <br /> jll ./Avr���'f <br /> Original source:Houk and Bray 1977 <br /> Hayden Gravel GS-1 a' <br />