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GEOTECHNICAL STABILITY EXHIBIT EXHIBIT U <br />There are no buildings or any structures outside the permit area which could be affected by the <br />excavation. A minimum fifteen foot buffer will be maintained from the permit boundary line to <br />all excavations. All reclaimed areas will be restored to relatively flat (<3.5%) slopes except for <br />the side slope, which be mined to a 1.514:1 V and reclaimed to a 3H:1 V slope. The surface <br />material of these slopes will be topsoil. During placement of the backfill material, the operator <br />will compact using standard earthmoving techniques. <br />The soil type of the overburden and waste fines used in the backfilling of the side slopes will <br />range from sand-silt-clay with slightly plastic fines to inorganic silts and clayed silts. <br />Design factors <br />In the extremely remote case that a slope failure would occur, if the slope failed up to the Qwest <br />Communications Line (the closest man made structure to the operation), Figure U-1 shows the <br />slope angle that would occur. The horizontal distance from the edge of the excavation to the <br />communications line is 70 feet. The failure angle would be 8 degrees or 7.114:1 V. This angle is <br />far milder than normal failure angles in material that gets strength from internal. angle of friction. <br />Figure U-2, from Huang, shows typical internal angles of friction for various materials. <br />Assuming that the gravel is classified as GC, clayey gravels, poorly graded gravel - sand - clay, <br />this material has an internal angle of friction of approximately 34 degrees. <br />Simmons Pit, March 2009 U-1