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IECO and other subcontractors for earlier studies. For this study on refuse <br />material stability, samples were obtained from the refuse piles near the • <br />mine portal and warehouse. <br />Soil Shear Strength <br />Based on saturated direct shear tests by IECO on undisturbed samples, the <br />cohesion ranges from 0 to 300 psf and the friction angle ranges from 10 to <br />50 degrees. See Appendix A. <br />These strength parameters for the soil material were also confirmed by back <br />analyses of slides as discussed in the following sections. These parameters <br />are important because the colluvium serves as the foundation for the <br />proposed refuse pile embankment. lECO's calculations used a cohesion of <br />2000 psf and a friction angle of !0 degrees for the colluvium while later <br />tests and studies confirm a limiting value of 300 psf and 30 degrees. <br />Additional slope stability calculations of the most recent active slides also <br />converged to strengths of 300 psf and 30 degrees for cohesion and friction, <br />respectively. These values are shown in Table 1. <br />TABLE 1 • <br />SOIL PROPERTIES COMPARLSON <br />Year Tested <br />1976 1980 1984 <br />Cohesion 2000 psf 300 psf 300 gsf <br />Internal Friction !0° 30.5° 30 <br />Dry Density 125 pcf 120 pcf 100 pcf <br />Computations were also performed using the lower strengths indicated in <br />the direct shear tests. <br />Refuse Material <br />The samples gathered from the refuse piles are described in Appendix C. <br />Twenty shear tests were performed on drained, consolidated, and saturated <br />refuse material samples. Of the seven groups of samples, three consistently <br />exhibited a narrow range of 29° to 33° friction angle (F1-3, F1-4 and Fl-7j <br />-16- • <br />