Laserfiche WebLink
<br />analyze two possible modes of failure with the geologic conditions indicating slope <br />behavior will most likely be intermediate between the two models. <br />In our opinion the circular model represents a conservative case. The wedge <br />model indicated much higher factors of safety if structure controls. We believe the <br />structure will have a significant influence and have considered this in formulating the <br />slope recommendations presented below. Based on experience in the East Pit and <br />the results of our analysis, we believe relatively steep overall slope angles are <br />possible for the north and side walls of the West Pit. Wfth a fairly competent rock <br />mass, reasonable water conditions and a flat or favorable bedding orientation, both <br />models indicate stable conditions. The stability of the slopes has been field tested <br />to a degree with experience in the East Pit over a number of years. The East Pit <br />working face has progressed up-dip (with the bedding planes dipping out of the <br />face) for about 18 years without a significant slope or even bench failure. <br />• The results of the analysis are valid for the conditions modeled. The primary <br />factor which could cause instability is water. Our models included a conservative <br />water condition with saturation of 1/2 the height of each coal interburden. Other <br />factors which could result in unstable conditions include undercutting or overhangs <br />or the presence of very low strength bentonitic layers. The slope should be <br />regularly monitored to identify evidence of movement or tension cracks. Water <br />should not be allowed to stand or pond near the top of the slope. <br />The following slope recommendations are based upon our judgement of the <br />conditions and the results of the analysis. <br />1. A maximum overall slope of 65 degrees is recommend for the north <br />wall of the West Pit between the X-Floor and the F-Floor. As shown on <br />Fig. 2, typical interburden bench angles and bench widths will result <br />in production face angle on the order of 62 degrees. <br />I 1 <br />COLOWYO COAL COMPANY, L P. <br />CTLT 23,595 t 6 <br />