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lY. STABILITY INVESTIGATIONS FOR THE RECLAMATION OF FACILITIES WITHIN <br />THE AND LIDE AREA <br />' A. Introduction: <br />' The portal bench, portions of the main access road, the shop warehouse pads and <br />the substation all lie within the Landslide Boundary and are characterized by an <br />upslope cut and a downslope fill, both of which must be retained. There are a <br />' number of available construction alternatives for returning these areas to their <br />approximate original contours (AOC). This investigation has focused on <br />determining which variation or construction combination would lead to the most <br />stable reclaimed slope. The possible variations which were considered were the <br />' following: <br />1. Backfill of cut areas <br />a. Backfill to be compacted to 95% of maximum standard proctor <br />density <br />b. Backfill to be compacted to SS% of maximum standard proctor <br />' density <br />2. Dewatering system <br />a. No dewatering provisions after reclamation <br />b. Dewatering system to be left for permanent operation after <br />' reclamation <br />3. Retaining wall system <br />a. Retaining walls to be removed and salvaged <br />b. Retaining walls (for cut slopes only) to be buried in place to improve <br />final slope stability. <br />' To allow the retaining wall system on the downslope (for fill side) of the road or <br />building site embankments to remain in place would be contrary to the ~' <br />requirements of returning those areas to their approximate original contours. , <br />Therefore, this study considered burying in place only those retaining walls on the <br />upslope (or cut side) of the excavated areas. <br />H. Stability Program Description: <br />' The stability analyses for these reclamation alternatives was performed using a <br />slope stability computer program (Slope In developed by Geo Slope Programming, <br />' Ltd., Regina, Soskatchewan. The simplified Bishop Method of slices was used to <br />solve for the factor of safety in each case. <br />The computer can assume any failure surface for the analyses. A circular failure <br />surface is normally assumed unless bedrock is encountered. [f a slip circle <br />intercepts bedrock, the failure is assumed to proceed along the top boundary of the <br />bedrock for that portion within the boundary of the failure circle. <br />t The computer automatically divides the failure section into slices and solves for <br />the factor of safety against sliding along that failure surface. Many possible <br />' failure surfaces are evaluated within an established grid. The critical failure <br />surface is that which produces the lowest factor of safety. Initially, a course grid <br />is used to establish a general vicinity of the critical radii coordinates. The grid is <br />then refined and centered in this area to converge on the absolute minimum factor <br />oP safety. <br />4 <br />