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• -19- <br />configurations from Sta. 0 +00 to about Sta. 8 +50. The configuration depicted <br />for Sta. I0 +00 is fairly typical for the remaining: portions of the pit. These <br />configurations were analyzed for stability and are presented in Appendix C. <br />Our geologic field survey indicates that the bedrock within the highwall <br />dips between 5 and 10 degrees. An isopach of the top of the Wadge coal seam <br />provided by Colorado Yampa Coal Company indiciates that the seam dips downward <br />to the northwest at about 6.5 degrees in the immediate vicinity of the pit. <br />We used a bedrock dip angle of 6.5 degrees in our analysis. <br />The physical configuration and extent of the spoil and bedrock can be <br />fairly well defined based upon available information. The major unknown is <br />the thickness and extent of a layer of the fire clay. Fire clay was observed <br />below the coal seam in one of our test pits. We assumed a 1 -foot thick zone <br />• of fire clay occurred over the entire area, between the bottom of the spoil <br />and the surface of the relatively intact bedrock. This assumption was made <br />to evaluate whether or not the materials exist in sufficient extent to affect <br />stability and what affect the materials have on stability. <br />The results of triaxial testing prepared by Science Applications, Inc. <br />indicates that most of the intact bedrock in the area has angles of internal <br />friction greater than 30 degrees and unconfined strengths greater than 100,000 <br />psf. Considering that the bedrock is probably fractured and not intact, the <br />strength values indicated for fresh or intact bedrock should be reduced. For <br />our analysis, we used 0 of 20 degrees and a cohesion of 5,000 psf for the bed- <br />rock. <br />We made an analysis of highwall stability for a portion of the 8050 pit, <br />east of the investigated area, in January, 1979. The highwall in that analysis <br />