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Acz • Ms. Cathy Bcgcj January 14, 1992 Page 5 Table 1 SUMMARY OF MATERIAL PROPERTIES USED FOR STABILITY ANALYSES ProPeKl Refuse to Foundatbn Soil Or Unit Weight (pen SO pd 120 per Friction Angle (~ a]° 30° Conesion (par) o par tooo par \ore 1 - Material properties baud on values rtponed by GwWest (1968) baud on field and laboratory testing Dote 2 - Material properties baud oa creamed wlues, Rocty Mounuin Geotechnical, Inc., (1962) We understand that tW-o connecting tmderdrains have been installed under the base of the pile to maintain water levels at or near the original ground surface. Therefore, we have assumed that there is no build-up of water pressure in the refuse pile. • 3.0 Stability Analyses Stability analyses were conducted on the two cross-sectiotu shown on Figure 2. Analyses were conducted utili~ a computerized slope stability model (XSTABL, Sharma 1991), that can search for the critical tirtular failure az well as the critical sliding block failure mode. The program utilvrs the modified Bishop's method and Janbu's method of analysis The critical failure planes for each of the cross-sections are shown on Figure 2. The results of the stability analyses are summarized on Table 2, Results of Stability Analyses. Table 2 RESULTS OF STABILITY ANALYSES Cross-Src~ion Minkoom Slatre Factor of Sakry Clmly Sliding Block Croac-section A-A' 27 25 erne-sertfoa aB' 27 25 Sttrfidal Cailttres were not analyrad, az these are considered to be maintenance concerns rather than overall slope failures that could impact the performance or operation of the refuse pile. Therefore the search routine was limited to arcular failures that would encompass the entire slope. If stn-Cicial failures were conidered, an infinite slope failure model would be used and would predicate a factor of safety of 2.0 for [he 3H:1V slopes tomposcd of fine refuse with a friction angle of 33 degrees • Computer printouts of the stability analyses are presented in Attachment A. Review of the results indicates that the factor of safety calculated for the etactittg pile configuration is generally greater than that calculated [or the original refuse pile (Geo-Testing Laboratories, Inc, 1981 and Rocky Mountain Geotechnical, 1982). This is primarily the result of the flatter side slopes. The original analyses assumed that 2H:1V side slopes would be conswded. However, both the current and planned Cmal topography of the pile indicates 3H:1V sidt slopes. In additioq actual laboratory testing on the fine refuse material indicated slightly higher sUength properties (GeoWest, 1988) then previously azsumed.