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To DRMS Den Page 5 of 5 2017-07-12 22.12 51 (GMT) 13032008630 From Greg Lewicki <br />Geotechnical Stability Exhibit <br />The permanent slopes in puce at the Hayden Gravel Pit will be 3H: IV or shallower as sho-wn. on <br />Map F of the approved permit. <br />From Table 2.5 it the SMS; Mining Reference Handbook". thv backfill is best classified as loose <br />sand, r axed grain size. This material has an internal angle 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 assurned internal angle; of friction of 34 dq,,rees car be approximated by <br />ignoring the cohesion component of the stability and simply evaluacing the internal angle; of <br />friction as follows: <br />FOS -_ _Tari-ert of'latenial Angle of Friction <br />Tangent of Actual Angle of Failure SLirface <br />Tan 34' 0.6745 <br />FOS - - _ -- ------- - -.0- <br />Tan 18.4° 0.33)26 <br />The permanent slopes at the Whitu River City Pit will be stable, and not risk <wy neighboring <br />structures, <br />t` ;i'✓ •-Flt 7 �'` L <br />� .F � .1 ••s d .� i �jw° <br />a`SS�Y w�r.w••,� <br />'Original source: Houk and Bray 1977 <br />Hayden Gravel GS -1 <br />