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• -31- <br />previously made a detailed analysis of highwall stability analysis for <br />to 8050 pit during initial mining. That analysis considered a cut with <br />adverse bedding and concluded that temporary pit walls would be relatively <br />safe from major failures at 75 degrees but that slopes between 50 and 60 <br />degrees were considerably safer. Minor failures were anticipated at a cut <br />slope of 60 degrees. During mining, it was found that relatively few problems <br />developed for highwalls cut at 60 degrees or flatter while problems developed <br />at angles steeper than 60 degress. <br />We believe that minor failures should be expected for cuts as steep as <br />55 degrees even with the provision of a bench between the spoil toe and cut <br />crest and construction of a lined interceptor ditch. Becuase little information <br />is presently available in regard to joint orientations of the rock, the above <br />• analysis should be considered to be preliminary and used for planning purposes <br />only. A detailed analysis should be made when some cutting of the rock is <br />accomplished and joint patterns can be readily observed. <br />SURFACE DRAINAGE <br />Observation by the Colorado Yampa Coal Company over the years indicates <br />that much of the precipitation which falls on the spoil surface upslope of <br />the pit tends to infiltrate the spoil and manifest itself in seeps or springs <br />at the spoil toe. Prevention of this infiltration would be both unreasonable <br />and economically prohibitive. Therefore, we believe that provision should <br />be made to intercept seepage at a point which will result in the least amount <br />of potential instability of the spoil bank and to reduce the amount of in- <br />filtration which takes place upslope. It is our opinion, that a surface <br />