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Maximum grade was kept to 10 percent or less. All design grades comply with requirements of Rule <br />4.03.1(3)(a). Detailed design will be conducted at all switchbacks as part of construction drawing <br />preparation and any necessary adjustments will be made to keep maximum slopes at 15 percent or <br />less. <br />4.7.2 Slope Stability <br />Haul roads were located on the most stable slopes available, as required by Rule 4.03.1(2)(a); <br />however, due to the steep natural slopes in the areas where haul roads must be constructed, additional <br />geotechnical measures will be required in some areas to establish stable slopes. A slope stability <br />analysis was conducted in accordance with a method developed by D.W. Taylor and W. Fellenius for <br />the anticipated range of soil conditions and the design slopes. The method is presented in <br />Appendix H. Calculations with this method are based on a range of cohesion for colluvium soils <br />anticipated in the construction area. Cohesion values were obtained from tests conducted on site <br />colluvium soils collected primarily in the vicinity of the primary coal handling facilities. The <br />minimum values shown in the calculations are for a cohesion value that 90 percent of colluvium tests <br />are expected exceed, based on a statistical analysis. The maximum values shown in the calculations <br />are for a cohesion value that 10 percent of colluvium tests are expected exceed. <br />4.7.2.1 Cut Slopes <br />Cut slopes will be excavated to an overall slope of 1.5H: 1V when excavated in soil, or at a slope of <br />0.25 H: 1V when in rock, as required by Rule 4.03.1(3)(d). Cut slopes will be excavated in benches <br />to minimize the amount of excavation, as shown on the permit drawings. Slopes between the cut <br />slope benches excavated in soil will have a slope of approximately 0.5H: 1V. These cut slopes are <br />designed to achieve a factor of safety of 1.5 or greater as required by the Rules. Figure 4 -1 shows <br />maximum stable slope heights using the design method described above. Some slopes shown in the <br />permit drawings exceed the maximum allowable slope height based on the lowest cohesion value <br />used in the analysis. Additional geotechnical investigation and design or other slope stabilization <br />methods will be needed prior to haul road construction in these areas. The approach to establishing a <br />safe slope in such areas will include the following steps. <br />1) Investigate the road alignment to determine depth to bedrock. <br />a. If cut slope is in rock: <br />Revised March 19, 2010 <br />-3 ! / 6 <br />PAMpls\06 CO\26 \06261003 MCC Refuse Pile Site Review & Permit\WorkFiles\Permit Application \Text\2010- 08- 31_RPE East Permit Application <br />MR.doc <br />A1Q -34 $ 9 /'7/r0 <br />