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N. ~,ST.ABILITY INVESTIGATIONS FOR THE RECLAMATIOt7 OF FACILITIES WITHIN ~ lriL AN SLIDE r1REA ~• A. Introduction:' The portal bench, portior~ of the main access road, the shop warehouse pads end thE: substation all lie within the Landslide Boundary and are characterized by an upslope cut and a downslope fill, both of which must be retained. There are a number of available construction alternatives for returning these areas to their approximate original contours (AOC). This investigation has focused on determining which variation or coc~struction combination would lead to the most stable reclaimed slope. The possible variations which were considered were the following: L Backfill of cut areas a. Backfi7l to be compacted to 95% o! maximum standard proctor density b. Backfill to be compacted to 85% of maximum standard proctor density 2 Dewatering system a. No dewatering provisions alter reclamation b. Dewatering system to be left for permanent operation alter reclamation 3. Retaining wall system a. Retaining walls to be removed and salvaged b. Retaining walls (for cut slopes only) to be buried in place to improve ~ final slope stability. ~, To allow the retaining wall system on the downslope (for Pill side) of the road or building site embankments to remain in place would be contrary to the requirements of returning those areas to their approximate original contours. Therefore, this study considered burying in place only those retaining walls on the upslope (or cut side) of the excavated areas. B. Stability Program Description: The stability analyses for these reclamation alternatives was performed using a slope stability computer program (Slope In developed by Geo Slope Programming, Ltd., Regina, Soskatchewan. The simplified Bishop Method of slices was used to solve for the factor of safety in each case. The computer can assume any failure surface for the analyses. A circular failure surface is normally assumed unless bedrock is encountered. If a slip circle intercepts bedrock, the failure is assumed to proceed along the top boundary of the bedrock for that portion within the boundary of the failure circle. The computer automatically divides the failure section into slices and solves for the factor of safety against sliding along that failure surface. Many possible failure surfaces are evaluated within an established grid. The critical failure surface is that which produces the lowest factor of safety. Initially, a course grid is used to establish a general vicinity of the critical radu coordinates. The grid is then refined and centered in this area to converge on the absolute minimum factor of safety.