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i~ <br />MEMORANDUM <br />T0: KACrofts <br />~• <br />999 <br />pEC 15 1980 <br />MINEDpL~pA7N~Dp~RECLAMAl10N ;COAL <br />COIA, Y'KDPI: tUTU~1E5OURCES- <br />RE: Bond Release Area D at Energy Mine No. 3 DATE: 12/5/80 <br />You have asked me to respond to the slope stabillty concerns in <br />connection with Bond Release Area D that Bob Liddle and Mike Savage <br />expressed in their letter of November 26, 1980. <br />During our visit to the site on December 4, 1980 to inspect the <br />cracks, we found that the cracks are primarily small scarps with about 8 <br />inches of displacement and are located in a linear zone that corresponds <br />very closely [o [he location of the final highwall. <br />The attached cross-section depicts the pre-mining land surface, the <br />post-mining land surface, the Location of the ldadge seam and. the location <br />of the final highwall. Notice how the zone of cracks is located im- <br />mediately above the final highwall. <br />The following discussion responds to each of the specific concerns in <br />the letter from Boh and Pfike: <br />1) Cause of the fractures. -- <br />Based upon examination of the attached cross-section and field obser- <br />vations, I am confident that the cracks are caused by differential <br />settling due to the abrupt change in spoil thickness at the final <br />highwall. Immediately upslope of the highwall, the spoil thickness <br />is approximately L20 feet. Immediately downs lope of the highwall, <br />the spoil thickness is only 20 feet. <br />2) The stability of the slope on which [he fractures occurred; and 3) <br />the potential for further occurrence of settling, downslope movement <br />and rotational movement. -- <br />