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• Morrison Knudsen Corporation October 10, 1996 Page 3 (SF) of 1.7 and 1.9 for sections A-A and B-B, respectively. For the purpose of evaluating long- term stability we also modeled conditions consisting of the phreatic surface at the ground surface and of increased pore pressures. For these cases the SF ranged from 1.6 to 2.1, well above the required value of 1.3. In general the stability of the reclaimed slopes is less sensitive to variation in ground water or pore pressure and more dependant on the shear strength of the soil. In general, the subsurface conditions modeled in the stability analysis were conservative. Bedrock was modeled at an elevation of about 20 feet lower than that indicated from the borings. The location of ground water was also modeled far more conservatively than what the borings would suggest. In summary, we are of the opinion that although effective stress parameters were not used, the resulting safety factors determined by this analysis are conservative and well in excess of the required factor of safety of 1.3. We believe that if the reclaimed slopes are properly constructed as described below, stability should not be a problem. Fill Recommendations: Reclaimed fill slopes should be no steeper than 3:1 overall. All fills should be placed on ground that is completely cleared of vegetation and root growth. Where available, boulder rubble with a wide range of sizes would be acceptable for use as a starter fill • at the toe of the fill. Where boulder rubble is used as a drainage feature beneath a Fill, it should be protected from fines migration by either a filter fabric or a suitable filter course. If rubble is placed in areas not intended for drainage, it is important the rock be irrcorporated into a soil matrix to insure that any voids between rock are filled to prevent migration of fines. Proper drainage of reclaimed fill slopes is critical to long-term performance. Any drainage features located above the fill should be intercepted and diverted away from the fill. Any surface water conditions that may develop on the cut slopes should be drained. The existing cut slope benches could be used in conjunction with a drainage system. The face of the reclaimed slopes should be properly revegetated and constructed to allow for adequate drainage to prevent oversteepening of the slopes due to erosion. We recommend the fill material be placed in horizontal lifts, adjusted to a moisture content at or above optimum moisture and compacted to at least 85 % of the maximum modified Proctor density. It is important that the reclaimed slopes be keyed into the existing cut slopes. Our previous study recommended benching the cut slopes at intervals on the order of 8 to LS feet in height. These existing benches may be used for placement of fill provided they are first cleared of any sloughed or eroded material and properly prepared. We believe additional benches are necessary to adequately key the fill for the reclaim slopes, We recommend additional benches be cut every 4 to 5 feet of slope height. The benches should be at least 4 feet wide. The bench surface should be prepared by scarifying to a depth of 8 inches, adjusting the moisture content • to at or above optimum and compacting to at least 85% of modified Proctor density.