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11r. Trw ltnArmn O~~Ger 1(inina CanrPmry Oi/li/00 Parr? /~ / ' • Materials For the stability analyses, three different types of materials were Considered The following materials were modeled: • Engineered Fills: These materials will be obtained primarily from the upper and crntnl portions of the existing sGdc on the west side of the Elk Creek valley. Materials will be placed in controlled lifu and compacted to form the bench Fills. These materials will typically consist primarily of fine-gained cohesive soils. • Subgnde: The existing subgnde is part of the Maa Verde Formation and atypically afine- gnined cohesive soil derived from and including colluvial sandstone shale materials. Soil: Soil will be stepped from the faalities arcs poor to the disturbance. These mateeak will be placed in the stockpile for later use doting reclamanon operations. Soil materials will be moderately cohesive, strong, loam soils. Strength Parameter The engineered (ill strrngth parameters used for the stability analyses aze based on consolidated undrained ttiaaial testing, included in Attachment A, completed by Advanced Tem-Testing of Denver, Colorado. [n order to be conservattve, the results used in these analyses aze based on residual strrngth values. In addition, the triasial test was performed on a supple deemed to be Erom the weakest soil unit on the site. Strength parameters for the subgnde and soil stod~ile are based on test results from the engineered fill tttateaals, prcviotu testing of similar materials for the West Valley Fill (Lincoln DeVore, 1997), published values, and our enpftteering judgement. The following s~~~*+r++°~~es the strength parameter used in the stability analysis for these materials modeled: • Engineered Fills: Isbontory consolidated undrined triazial testing aPas completed on the nuterial to determined it's potential shear sttetrgtlr. The results of this testing indicate this material has a retompacoed moist density of 130 pcf, a residual effective stress Fecdon angle of ~' = 26.7°, and acohesion = 752 psf. However, for this analysis, an effective saes faction angle of ~' = 26.7° and a cohesion of 400 psf teas toed to be conservative. Subgnde: The material wu assumed to have a moist density of 120 pcf, a ~ = 26°, and a cohesion = 250 psf. In a report produced by Abd in 1998, the density of this material wu assumed to be 150 pcf. A lows density wu usigned to this material to remain conservative. The subgnde wss assigned a cohesion less than the cohesion of the engineered fill material Material properties were sssumed hued on geologic origin, descapdon of the materials, tat results for the slide matemis, report prepared by Abel 1998, and previous testing of similar materials for the West Valley Fill. • Soil This material was assumed to have a moist drnsity of 120 pcf, a ~ = 26°, and a cohesion = 250 psf. The density was speafied to be equal to that of the sttbgnde ustrmirtg that saaper will place it in thin lifts. • -