Laserfiche WebLink
<br />• features9. The slopes under consideration are on the order of 250 to 350 feet in <br />height which would require a joint spacing on the order of 2.5 feet or less. <br />Observation of the rock above the C-Seam indicates this condition would be met <br />more often than not. Since the fractures and joints are not randomly orientated, this <br />is considered a conservative assumption. The actual slope will probably perform in <br />a manner in between the structurally controlled but low strength wedge model and <br />the higher strength but more direct failure surface of the circular model. <br />Strength envelopes for the rock mass were estimated using two methods. <br />Based upon visual observations and review of the previous investigations a rock <br />mass rating system (RMR) was used to estimate a strength envelope". This rating <br />was adjusted for blasting damage'. The rating of the rock mass was slightly above <br />the strength envelope for "fair" rock shown on Fig. B-3. <br />The working face of the East Pit has been steepened over the 18 years of <br />• operation based upon experience. The working face has an unfavorable dip angle <br />with the bedding dipping out of the face at about 5 degrees. The lower portion of <br />the working face consists of a steeper section about 130 feet in height with an <br />overall slope angle of about 65 degrees. We assumed water to 1/2 the interburden <br />height. We then back-calculated a strength envelope which produces a factor of <br />safety of 2. This envelope is slightly above but close to the fair envelope estimated <br />using the rock mass rating system as shown on Fig. B-3. We believe the close <br />correlation of these overall strength envelopes is a positive indication of the validity <br />of both methods. <br />The circular method was then used to evaluate three slope geometries and <br />to consider the effects of spoil pile location. Graphic results of the stability analyses <br />are shown on Figs. B-4 and B-5. We evaluated the stability of the north wall (250 <br />foot height) and the east and west walls (350 foot height) for various slope angles <br />with 1/2 water, and with and without the 0.05 pseudostatic coefficient The typical <br />section analyzed is shown on Fig. 2. The results of the analysis are shown on Fig. <br />COLDWYO COAL COMPANY, L P. <br />crux zases 14 <br />