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• layers with the coal waste pile underlain by clay soils and then bedrock. The depth <br />to bedrock was 7 to 23 feet in our borings and test pits. A bedrock layer at a <br />constant depth of 30 feet was assumed in the model. The configuration of the <br /> <br />models can be seen on the stability output figures in Appendix C. We do not believe <br />previous surface mining extends into the area of the proposed pile, However, the <br />\,,.Or~ surface mining apparently extended close to the valley centerline and N is <br />--~~~' ~ conceivable that a portion of the proposed RDA is underlain by reclaimed spoil. If <br /> <br />this condition exists it will be revealed during excavation of the toe buttress. In any <br />case, the presence of spoil below the RDA was analyzed. For this model a bedrock <br /> <br />layer was not included. <br />Numerous cases were evaluated for various soil types, strengths and <br />s <br />• considering water and possible ground accelerations. For each case infinite slope <br />type conditions were evaluated and circular failure surfaces were analyzed. Block <br />sliding type failures were checked for several models and circular failure type <br />conditions were determined to be more critical. Computer aided stability analysis <br />was performed using the program Geoslope (tm) developed by Geocomp Corp. <br />(Reference 14). This computer program is based upon the slope stability analysis <br />procedure STABL developed at Purdue University. Geoslope offers Modified Bishop <br />Analysis Methods for circular-shaped failure surfaces. The following sections <br />discuss the selection of soil strength parameters, description of the cases analyzed <br />and the results of the analysis. <br /> <br /> <br />• <br />Coal Waste Properties. Coal waste properties were analyzed based <br /> <br />upon laboratory testing of bulk samples and review of reference material. <br />• Some variability of the coal waste will occur as mining progresses; waste <br />9 <br /> <br />