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- 12 - <br />materials have an average drained friction angle of approximately <br />28.5° and a drained cohesive strength of approximately 350 psf. The • <br />drained shear strengths of these materials range from 26° to 30°, and <br />the cohesive strength varies from 200 to 500 psf. <br />REFUSE E1~7BAN(Q9FNP STABILITY <br />Coal Refuse FSnbanlanents: Coal refuse will be disposed of in the <br />sub-areas shown on Fig. 3. Zlie coal refuse is estimated to have the <br />approximate gradation shown on Fig. 6 and a final iroisture content of <br />108 to 158 when placed in the disposal area. <br />The refuse will be placed in lifts not to exceed 24 inches in <br />thickness and will be canpacted to attain 908 of the maximum standard <br />Proctor density according to AFtiS[~'i0 Specification T-99-74. The height <br />of the proposed coal refuse piles will vary between 50 and 90 feet. • <br />Exterior slopes on the refuse pile will vary between 3 to 5 horizontal <br />and 1 vertical, - <br />Selected Design Values: 'lt~e design values selected for the natural <br />foundation soils at the site are: Unit weight, 115 pcf; friction <br />angle, 26°; cohesion, 0 psf; and pseudostatic earthquake coefficient, <br />0.059. The design strength values selected are lower than the lowest <br />strength parameters obtained in the laboratory testing. Since very <br />low excess pore pressures developed during the triaxial tests and the <br />er~anlanent will be constructed at a relatively slow rate, a single <br />analysis was ctxiducted for the end of construction case and long-term <br />stability. In our opinion, the foundation soils will essentially <br />u <br />