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~~ quently modified by S. Chirapuntu in 1974, C. Jude in 1976 and 1977, and by <br />KCKA in 1977. The program calculates [he factors of safety for specified <br />circular slip surfaces, or searches for the circular slip surface having the <br />minimum factor of safety using the Bishop's Modified Method. The factor of <br />• <br />safety calculated by the Ordinary Method of Slices is also given for each <br />circle. The program may be used for total or effective stress analyses, or <br />a combination of both, and with or without seismic forces. The units used <br />in the program are pounds and feet. <br />For this study we used a total stress analysis and an estimated phreatic <br />surface, without seismic forces. We selected various elevations ("tangents") <br />throughout the backfill slope for which we had the computer search for a <br />minimum factor of safety. The program analyzed a total of 143 circles for <br />Section A and 204 circles for Section B. The resulting minimum factors of <br />safety for each section and their corresponding failure surfaces are por- <br />trayed in Figures 3a and 36, Calculated Minimum Factors of Safety and Failure <br />Surfaces. <br />RESULTS <br />Profile "A" <br />As shown in Figure 3a, the minimum static factors of safety calculated <br />were 1.5 and 1.8 for the failure surfaces shown. <br />IC should be noted that the 1.5 factor of safety was calculated for a <br />near-surface portion of the fill slope which approaches a 1~:1 and up to a <br />2:1 slope ratio as shown on the provided drawings, This is a localized <br />situation only. The general minimum static factor of safety for a slope of <br />3:1 would be 1.8. The potential failure surface, as should be expected, <br />extends from near the top of the slope, down to the base of the surficial <br />soil layer overlying bedrock and terminates near the toe in the sedimenta- <br />tion basin. <br />Profile "B" <br />As shown in Figure 3b, the minimum static factor of safety calculated <br />was 2.4 with a failure surface located along the shear plane. <br />• As might be expected, the potential failure surface is anticipated to <br />6 <br />KENNETH C. KO & ASSOCIATES <br />