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In its review, the CMLRD expressed a concern regarding <br />lateral stability of the F-seam due to the loading of the <br />waste pile. As noted in the previously submitted applica- <br />tion, the F-seam is overlain by 200 to 230 feet of overburden <br />comprised of 50 to 70 feet of colluvium and 130 to 160 feet <br />of bedrock. <br />In order to determine the effect of the refuse pile on the <br />partially mined F-seam, a detailed and complicated geotechni- <br />cal analysis would be required. However, as discussed with <br />the CMLRD, a very conservative, simplified analysis would be <br />completed to first screen the pile's effect. This analysis <br />basically involves a two dimensional wedge type failure <br />surface through the partially mined F-seam. <br />The following assumptions were made in the analysis: <br />Ultimate configuration of the waste pile at elevation 6880 <br />feet. <br />There are no plans for secondary mining (full extraction) <br />near this portion of the main entries; i.e., the coal will <br />be mined partially, leaving a majority of the coal in the <br />form of pillars. However, to simplify the analysis model, <br />it was assumed that the F-seam is completely mined which <br />is very conservative. <br />The mine plan calls for barrier pillars at the main <br />entries. However, to simplify the analysis model, it was <br />assumed that the slip surface occurs at the F-seam floor <br />and extends until it intersects the existing ground <br />surface or outcrops. <br /> <br />• ' <br /> <br /> <br />r <br />i <br />• <br />21 <br />