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6. Slope Stability Analyses <br />If backfilling to original contour is considered, many different <br />backfill angles would be employed. However, since so much of the <br />area is in very steep terrain, it is reasonable to consider a steep <br />angle for the backfilled area. An angle of 45 degrees is assumed. <br />Exhibit 3 shows the geometry for two typical cases of the <br />backfilled roads. Case 1 assumes that the outside edge of the road <br />is compacted fill but not solid rock. Case 2 assumes that the <br />entire road surface rests on solid rock which will be the <br />foundation for the f i l l . Both cases can be expected for reclamation <br />to approximate original contour. <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 />#1 and #2 Mine Road <br />(Bin Pad) <br />#3 Mine Road <br />#4 Mine Road <br />#5 Mine Road <br />Cohesion F. Angle Density <br />lb /sq.ft Degrees lb /cu.ft. <br />700 36 .0 °; 114 <br />550 44.0° 122 <br />0 51.0° 111 <br />730 34.0' 118 <br />* denotes peak strength parameters, not residual. <br />Using the above parameters, the slope geometries of Exhibit 3 and <br />different pore pressure ratios, various cases of slope stability <br />have been modelled using the REAME program developed by Dr. Yang <br />Huang of the University of Kentucky for rotational failures. The <br />program uses the Bishop's method of slices to determine the minimum <br />factor of safety for a given set of conditions. Rotational failure <br />is the most likely method of failure because it has the most mass <br />per unit surface area for this geometry. Translational or plane <br />failures generally occur on long slopes where there may be a <br />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 />1 1 <br />