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GEOTECHNICAL STABILITY EXHIBIT <br /> There are no buildings or structures outside the permit area that could be affected by excavation. <br /> Sufficient buffers will be maintained to neighboring property lines. For the purpose of this <br /> stability analysis, only processed material that is backfilled to the final 3H:1 V slope is evaluated. <br /> All other materials and slopes are either short term (active highwall), medium term but excavated <br /> in more stable material (mining slopes at 2H:1 V that are unbackfilled), or gentler sloped <br /> (>3H:1 V). <br /> The material mined at the Box Creek Placer is an alluvial sand and gravel deposit. This material <br /> is then processed to remove gold. The removal of gold via sluices reduces the fines content of <br /> native alluvium. Therefore,the cohesive properties of the material are reduced. On this basis, <br /> from Table 2.5 in the SME Mining Reference Handbook',the material that most represents the <br /> processed alluvium that will be used in backfilling is sand and gravel (mixed grain size). This <br /> material has a minimum internal angle of friction of 45 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 with an assumed internal angle of friction of 45 degrees can be approximated by <br /> evaluating the internal angle of friction as follows: <br /> Tangent of Internal Angle of Friction <br /> FOS = Tangent of Actual Angle of Failure Surface <br /> Tan 45' 1 <br /> FOS = — — 3.01 <br /> Tan 18.40 0.333 <br /> The 3H:1 V slopes will be safe as the final condition. <br /> C <br /> Ben Langenfeld, P.E. ez'c 00471511 <br /> ��SSIOtJA1.��G`� <br /> Original source: Houk and Bray 1977 <br /> Box Creek Placer Mine Greg Lewicki and Associates,PLIA' <br /> September 2018 GS-1 <br />