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of the proposed sedimentation basin for our analyses. The toe of the proposed <br />~• <br />fill will be located immediately upslope of this basin allowing the foundation <br />soils to become saturated with time. We have used a conservative estimate of <br />the ground-water level in this area. <br />The results of our analyses, in summary, indicate adequate long-term, <br />static stability for the proposed slope ratio of 3:1. The provided drawings, <br />however, depict slope ratios of about 1~Z:1 up to 2:1 for areas near the sedi- <br />mentation basin. We suggest that all slopes be laid back to a minimum slope <br />ratio of 3:1. <br />SCOPE OF WORK <br />• <br />The scope of our services for this study has been to analyze by computer <br />methods the anticipated static factor of safety against failure of the pro- <br />posed backfill slopes, IJe were to use the provided data (described previously) <br />For estimating the soil engineering criteria needed for [he analyses. We <br />understood that MLRB's minimum acceptable static factor of safety is 1.3. <br />STABILITY ANALYSES <br />From the provided data, we prepared two profiles of the proposed backfill <br />slopes in the vicinity of the sedimentation pond. The locations of these pro- <br />files are shown in Figure 1, with the profiles illustrated in Figures 2a and <br />2b. The profiles depict the la you[ of our coordinate system and sections, <br />estimated soil engineering properties, and the boundaries of the various <br />soil layers used in the analyses. The bulk density of fill was calculated <br />based on the assumed densities of constituent soil/rock materials and the <br />average bulking factor. Its friction angle was assumed to be 30°, compared <br />to the laboratory test results of 31.5° for the rock-on-rock friction angle. <br />A minimum amount of cohesion, 300 psf (about 2 psi) was assumed. For the <br />foundation soils, the friction was reduced to 27° and the cohesion was <br />assumed to be 1500 pcf (about 10 psi). The strength and physical properties <br />of bedrock were also given, to satisfy [he requirements of the computer <br />program. <br />The computer program used for our analyses was STABR, written by Guy <br />• Lefebre at the University of California at Berkeley in 1971, and was subse- <br />t <br />KENNETH C. KO & ASSOCIATES <br />