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Mr. Steve Magnuson <br />Mdy 6, 1987 <br />Page 3 <br />• (Kirkham and Rogers, 1981; U.S. Army Corps of Engineers, 1982; Uniform Building <br />Code, 1976; Algermissen et al., 1982). <br />MATERIAL PROPERTIES USED IN STABILITY ANALYSES <br />The material properties used in the stability analyses are given below; <br />Unit Weight (pcf) Shear Strength <br />----------------- ------------------------------------------ <br />Material Moist Saturated Cohesion (psf) Friction Angle (degrees) <br />1. Refuse 91 103 660. 30. <br />2. Sedimentary 120 135 4000. 50. <br />Rock <br />The rack properties are typical values for sandstones and shales, and were used <br />1n previous stability analyses (WWL, 1984). The refuse material properties <br />were based upon the geotechnical test results summari=~d in this letter. <br />The stability analyses were conducted assuming steady seepage conditions <br />(outlined in U.S. Army Corps of Engineers, 1982; and Wilson and Marsal, 1979). <br />Under these conditions, the shear strengths listed above were assumed to be <br />• effective shear strengths. <br />Pore pressures in the materials were represented by steady seepage conditions <br />governed by Laplace's equation (Cedergren, 1970). The phreatic surfaces in the <br />waste pile and foundation were essentially the same as those used previously <br />(WWL, 1984), and were estimated from a procedure developed by Casagrande (1937) <br />for flow -through homogeneous embankments (Cedergren, 1970; Lambe and Whitman, <br />1969). <br />STABILITY ANALYSIS RESULTS <br />The stability analysis results are summarized below and shown in Figures 4 <br />through 7. <br />Minimum Calculated Factor of Safety <br />----------------------------------- <br />Description of Case Static Pseudostatic <br />Low phreatic surface (at bottom of pile) 1.87 1.59 <br />High phreatic surface (at middie of pile) 1.61 1.44 <br />. The minimum calculated factors of safety are above Colorado MLRD criteria of <br />1.5 and 1.1 for static and seismic conditions, respectively. As mentioned <br />