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- 13 - <br />C <br />behave as granular materials under the loading conditions antici- <br />pated, and drained shear strength values are appropriate foc end of <br />construction and long-term loading conditions. <br />[3o coal refuse will be available for testing until the mine is <br />• <br />in operation. Therefore, in order to conduct the stability analysis, <br />an estimate was necessary for the strength properties of the coal <br />waste bank material. This information was obtained from the U.S. <br />Department of Interior Bureau of Mines Report of Investigation 8216 <br />"Physical Properties of t~stern Coal Waste Materials". This <br />publication presents drained triaxial and direct shear strength <br />information for three samples of coal refuse obtained at two mines in <br />the Western United States. The gradations of the thcee samples are <br />shown on Fig. 6 along with the estimated gradation curve for the coal <br />waste at the Deserado Mine. The following values were presented in <br />the reference for drained shear strength: <br />Drained Direct Drained Triaxial <br />Shear Shear <br />~ Cohesion ~' Cohesion <br />Mine Sample (psf) psf <br />Y YC)D 27.3 288 24.0 158 <br />Y YfD 26.5 130 19.8 778 <br />S SD 32.6 706 26.9 1,138 <br />Based on the published information and the grain size curve <br />estimated for the coal refuse from the Deserado Mine, we selected a <br />coefficient of friction of 22° and cohesirn values of 200 and 600 psf <br />for cohesion strength. Due to the granular nature of the Dual waste <br />L~ <br />