Laserfiche WebLink
• shale samples at the site. The model also included an unfavorable bedding <br />dip on the order of 5 degrees. <br />The model we used is shown on Figure B-1. In our initial analysis we retained <br />the unfavorable bedding used by Wahler to isolate the analysis on improved water <br />conditions. A model was analyzed using full saturation between coal layers and <br />"calibrated" to produce similar factors of safety as the Wahler model. The model was <br />then evaluated using saturation of each interburden layer to 1/2 height. We then <br />analyzed the model using no bedding dip. The results are shown on Fig. B-4. <br />The results show a significant increase in the factor of safety to above 2 for <br />steeper slopes either with the improvement in water conditions or improved bedding <br />dip. Much higher factors of safety are calculated if both improved water and dip <br />conditions are considered. The model would be expected to be very sensitive to <br />water conditions since water pressure in cracks behind the blocks is a major <br />component of the driving force. Considering the lack of consistent seepage or <br />saturation of the interburden in the working East Pit, we believe saturation to 1/2 <br />height represents a more realistic yet conservative estimate of water conditions. If <br />more favorable bedding dip conditions (0 degrees dip) are considered, then even <br />higher factors of safety on the order of 7 or more are calculated. <br />The stepped wedge method described above is very sensitive to water <br />conditions and bedding dip. The model is also dependent on assumptions regarding <br />the assumed overall angle of the failure surface. The model is useful to illustrate the <br />magnitude of sensitivity and provide information on stability conditions when <br />structure controls the failure surface location. <br />Circular Analysis <br />A circular analysis assumes that the slope is sufficiently fractured that a soil- <br />like circular failure surface is appropriate. This type of analysis may be appropriate <br />when the slope height is over 100 times the spacing of randomly oriented structural <br />COLOWYO COAL COMPANY, L. P. <br />OTL/T 23,595 1 3 <br />