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ACZ <br />Ms. Cathy Begej <br />January 14, 1992 <br />Page 5 <br />Table 1 <br />SUMMARY OF MATERIAL PROPERTIES USED FOR STABILITY ANALYSES <br />Properly Refuse ttl Foundation Soil (rt <br />Unit Weight (per) 50 pe( 1?0 psf <br />Friction Angle (°) 33° 30° <br />Cohesion (psf) 0 psf 1000 psf <br />Note 1 - Material properties baud on values reported by GeoWest (1988) based on ricld and laboratory testing. <br />Note 2 - Material properties baud on assumed values, Rocky Mountain Geotechnical, Inc., (19a2) <br />We understand [hat two connecting undcrdrains have been installed under [he base of the pile [o maintain <br />water levels a[ or near the original ground surface. Therefore, we have assumed [ha[ there is no build-up of <br />water pressure in the refuse pile. <br />3.0 Stability Analyses <br />Stability an:dyscs were conducted on [he two cross-sections shown on Figure 2. Analyses were conducted <br />utilizing a computerized slope stability model (XSTABL, Sharma 1991), that can search (or [he critical circular <br />failure as well as the critical sliding block failure mode. The program utilizes [he modified Bishop's method <br />and Janbu's method of analysis. The critical failure planes for each of the cross-sections are shown on Figure <br />2. The results of the stability analyses are summarized on Table 2, Results of Stability Analyses. <br />Table 2 <br />RESULTS OF STABILITY ANALYSES <br />Cross-Section Minimum Static Factor or Safety <br /> Circular Sliding Dlock <br />Cross-section A-A' 2.7 2.5 <br />Cross-action B-D' 2.7 2.5 <br />SurFicial failures were not analyzed, as these are considered to be maintenance concerns rather than overall <br />slope failures that could impact the performance or operation of the refuse pile. Therefore [he search routine <br />was limited [o circular failures [hat would encompass the entire slope. If surficial failures were considered, an <br />infinite slope Failure model would be used and would predicate a factor of safety of 2.0 for the 3H:1 V slopes <br />composed of fine refuse with a friction angle of 33 degrees. <br />Computer printouts of the stability analyses are presented in Attachment A. Review of the results indicates <br />[ha[ the factor of safety calculated for the e>asting pile configuration is generally greater than [hat calculated <br />for the original refuse pile (Geo-Testing Laboratories, Inc., 1981 and Rocky Mountain Geo[echnical, 1982). <br />This is primarily the result of the flatter side slopes. The original analyses assumed that 2H:1V side slopes <br />would be constructed. However, both [he current and planned final topography of the pile indicates 3H:1V side <br />slopes. In addition, actual laboratory testing on [he fine refuse material indicated slightly higher strength <br />properties (GeoWest, 1988) then previously assumed. <br />