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Slope Stability Case Analyses <br />Each portal area has its own geometry for the slope cases, which <br />are titled - Mine #3 Stability of Reclaimed Slope, etc. <br />From the CTL residual strength tests, the cohesions, angles of <br />friction and dry densities for each test are listed below: <br />Sample <br />Cohesion F. Angle Density <br />lb /sq.ft Degrees lb /cu.ft. <br />#1 and #2 Mine 700 39.0° 117 <br />#3 Mine 860 37.0° 108 <br />#4 Mine 1040 31.0° 117 <br />#5 Mine 400 38.0 115 <br />All results above denote residual strength parameters, not peak. <br />Using the above parameters, the slope geometries of each portal <br />area and different pore pressure ratios, various cases of slope <br />stability have been modelled using the REAME program developed by <br />Dr. Yang Huang of the University of Kentucky for rotational <br />failures. The program uses the Bishop's method of slices to <br />determine the minimum factor of safety for a given set of <br />conditions. Rotational failure is the most likely method of failure <br />because it has the most mass per unit surface area for this <br />geometry. Translational or plane failures generally occur on long <br />slopes where there may be a division between two soil types. <br />From standard seismic zone charts of the United States, it is <br />determined that the seismic coefficient for central Colorado is <br />0.04. <br />The highwall rocks in the Bowie Shale and the bench base in the <br />Rollins Sandstone do constitute a stiff base in which no failure <br />circles should pass. <br />The results of the various cases are shown in the following tables: <br />