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4.7.2.2 Embankment Slopes <br />Most of the haul road embankment slopes will be constructed on a side slope that exceeds 20 percent, <br />so all haul road embankments will be constructed on existing ground that is stepped back, or keyed if <br />constructed on bedrock, as required by Rule 4.03.1(3)(e)(ii), as shown on the permit drawings. <br />Embankments will be constructed in uniform lifts of 12 inches or less (loose thickness) and <br />compacted to a minimum of 90 percent of maximum standard Proctor dry density if the embankment <br />material contains less than 25 percent rock exceeding 6 inches in its largest dimension. If broken or <br />crushed rock is used for construction, the approximate average rock size will not exceed 36 inches. <br />Lifts will be limited to a maximum thickness of 36 inches. Embankment construction will meet the <br />requirements of Rule 4.03.1(3)(e), Paragraphs (iii ) through (viii). <br />Due to the steep slopes on which the haul roads will be constructed, embankment slopes have been <br />designed at a slope of 1.5H:1 V, as shown on the permit drawings, as allowed by Rule <br />4.03.1(3)(e)(ix). Embankment slopes have been evaluated with the same method as described for cut <br />slopes to comply with the minimum factor of safety of 1.3 required by the Rules. Figure 4 -2 shows <br />maximum stable slope heights using this design method. Some slopes shown in the permit drawings <br />exceed the maximum allowable slope height based on the lowest cohesion value used in the analysis. <br />Additional geotechnical investigation and design or other slope stabilization methods will be needed <br />prior to haul road construction in these areas. The approach to establishing a safe slope in such areas <br />will include the following steps. <br />1) Sample and test soils intended for use in constructing the embankment slopes: <br />a. Determine new maximum slope height based on actual test data from soils intended <br />for construction <br />b. If design requirements are met, construct slope as designed <br />c. If design requirements are not met, proceed to Step 2 or Step 3 <br />2) Design embankment with geogrid, crushed rock (1.35H:1V slope), or other geotechnical <br />stabilization method to achieve design requirements. <br />3) Embankment slopes not demonstrated to be stable in Step 1 or Step 2 will be stabilized with <br />other methods such as retaining walls, soil nailing, or other technology. <br />P.\Mp1s \06 CO \26 \06261003 RPE E Permit Mod Support \WorkFiles \Permit Apphcation \Text \Exhibit 82 RPEE design 2011 -07 -21 TR 127.doc 23 <br />