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• Seepage for the SWASE computer program is handled by <br />including a value for pore pressure ratio in the program. Pore <br />pressure ratio is defined by Huang as follows: <br />Volume of sliding mass under water X unit weight of water <br />ru = ----------------------------------------------------------- <br />Volume of sliding mass X unit weight of soil <br />To adequately account for any water within the slope, a pore <br />pressure ratio of .15 was selected for the SWASE stability <br />analysis. This is a conservative ratio indicating a much higher <br />water level than is believed to exist in the slope. This <br />conservative value for pore pressure ratio will result in a lower <br />factor of safety calculation. As shown on Figure 3, the factor of <br />safety for several trial failure surfaces of the existing slope <br />were determined using the basic parameters stated. To determine <br />the extent the out-of-pit spoil would have on the overall <br />stability of the slope, the same trial failure surfaces were run <br />with the addition of the out-of-pit spoil material and compared <br />with the stability calculated for the existing slope. Figure 4, <br />shows the calculated factor of safety of the slope with the <br />addition of the out-of-pit spoil. The factor of safety of the <br />slope was reduced somewhat with the additional weight of the <br />out-of-pit spoil, however, the overall slope stability shown in <br />• this analysis remained above the minimum factor of safety of 1.5. <br />Although some natural sloughing and erosion will occur over a <br />period of time in the creek bank, these small failures occur <br />naturally and were not considered in the factor of safety <br />calculations for the out-of-pit spoil stability analysis. <br />The third stability analysis was completed to determine the <br />affect of the out-of-pit spoil on the entire slope using the REAMS <br />computer program. As with the SWASE program, the existing slope <br />was analyzed bq calculating the factor of safety at different <br />locations within the slope. This is made possible in the REAME <br />program by adjusting the minimum depth of the tallest slice <br />considered. By increasing the minimum depth of the tallest slice, <br />the REAME program calculates the factor of safety of increasingly <br />deeper circles within the slope. Several trial computer runs were <br />made to determine the factor of safety at different positions in <br />the existing elope. <br />Since no surface seepage has been observed in the existing <br />slope, a phreatic surface at the top of the Wedge seam was used to <br />calculate the factor of safety within the slope. The calculated <br />factor of safety at several locations within the existing slope <br />are shown in Figure 5. The same parameters were used a second <br />time to calculate the factor of safety with the addition of the <br />out-of-pit spoil and compared with the factor of safety calculated <br />for the existing slope. As shown in Figure 6, the factor of <br />• <br />10 <br />