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Goodmiller #2 Pit 112 Permit <br />GEOTECHNICAL STABILITY EXHIBIT <br />There are no buildings or any structures outside the permit area which could be affected by the <br />excavation. A minimum 30 foot buffer will be maintained from the permit boundary line to all <br />excavations. All reclaimed areas will be restored to relatively flat ( <3.5 %) slopes except for <br />portions on the east side of the permit area, which be mined to a maximum 1.6H:1 V slope and <br />reclaimed to a minimum 3H:1 V slope. The surface material of these slopes will be topsoil. During <br />placement of the backfill material, the operator will compact using standard earthmoving <br />techniques. <br />The soil type of the overburden and waste fines used in the backfilling of the side slopes will range <br />from sand - silt -clay with slightly plastic fines to inorganic silts and clayed silts. <br />The worst case slope stability scenario exists during the mining, using the 30 feet buffer to the <br />permit area and the 1.6H:1 V mining slope. <br />Design factors <br />Figure 1, from Huang, shows typical internal angles of friction for various aggregates, sand, silts <br />and clays. Based on site inspections and drilling, the gravel material is clayey gravels, poorly <br />graded gravel — sand - clay, which is classified as GC this material, which has an internal angle of <br />friction of approximately 31 degrees. <br />In the extremely remote case that a slope failure would occur, if the slope failed up to the overhead <br />power line east of the permit area (the closest man made structure to the operation), Figure 2 shows <br />the slope angle that would occur. The horizontal distance from the edge of the excavation to the <br />edge of the property or the power line is 30 feet. This is the same approximate distance to the <br />power line. Using these parameters and a gravel depth of 40 feet, the failure angle would be 20.0 <br />degrees or 2.75H:1 V. This GC material will have basically no cohesion, due to the gravelly nature <br />of the material and will get all its strength from internal angle of friction. Based on drilling, the <br />entire 40 feet depth of mining will not encounter water so no phreatic surface needs to be <br />considered in the analysis. This angle of 20.0 degrees is far milder than normal failure angles in <br />material that gets strength from internal angle of friction. <br />Goodmiller #2 Pit Nov 2014 U -3 <br />