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DEL- MONT CONSULTANTS , INC. <br /> T7)k ENGINEER ING v SURVEYING <br /> _r = 125 Colorado Ave. . Montrose.CO 81401 . 1'970)249-2251 • {970}249-2342 Fat <br /> —;� www.det-rnont.cour • servtce0det-mont.corn <br /> GEOTECHNICAL STABILITY EXHIBIT—5875 Pit <br /> This site is for mining gravel. The average deposit is 25 feet thick. This is on a slope so the <br /> downhill side will daylight to natural ground and the uphill/cut slope will be 3:1. There are no <br /> buildings or any structures outside the permit area that could be affected by excavation. There <br /> are no neighboring properties to this mine site since it is in the middle of a large tract of land. <br /> From Table 2.5 in the SME Mining Reference Handbook, backfill is best classified as loose <br /> sand. This material has an internal friction angle of 28-34 degrees and no cohesion. This is <br /> worst case since the material will most likely be a mixture of sand and gravel which has an <br /> internal friction angle of 45-48 degrees and no cohesion. <br /> The Factor of Safety(FOS) for sides of the pit with a(3H:I V) 18.4 degree slope in loose sand <br /> material with an assumed internal angle of friction of 28 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 /> FOS=Tan28°/Tan 18.4°= 1.60 <br /> For a gravellsand mixture which is mostly likely what will be present the FOS would be: <br /> FOS =Tan 45°Iran 18.4°=3.00 <br /> The minimum safety factor in the permanent case is l.5,therefore the 3:1 slopes will be safe as <br /> the final condition for a worst case scenario of sand only. <br /> The nearest identified fault is more than 9 miles to the southwest. This permit is in an area of <br /> low seismic activity. <br /> �O�AD0 L1CF�,`tF <br /> Nicholas Barrett Izol I� <br /> PE 42106 pE 42106 <br /> �LSF 37 �--- <br />