APPCOR11061 - Laserfiche WebLink

Home Browse Search

The resulting excess overburden area will contain approxi- mately 210,000 cy of overburden, have slopes of 11~, (1V to 9H) and have a maximum elevat::on difference of 20 feet above original contours. The resulting stability calculations are based on the following parameters: Height (H) _= 20 ft. Slope (i) = 6° Specific weight (~) = 117 lb/ft3 Angle of internal friction (J~) = 35° Cohesion (c) = 100 lb/ft2 The angle of internal friction (~) and cohesion (c) are assumed conservative values. Figure 8 from Wyoming Fuel Company's April 14, 1981 application is used to determine the long term static safety factor for the stockpile. It would be inapE~ropriate to extrapolate from Fiqure 8 to determine a stability number (N) with such a small slope angle (6°); therefore, it will be demonstrated that a 6° slope has a safety factor in excess of 1.5. Safety Factor (F`;) = NC ~H N = Fs KH = (1.5)(117)(20) = 35.1 C 100 _ (Tang) (%~) (FI) _ (Tan 35°) 117(20) = 16.4 C 100 Using Figure 8 ar.d extrapolating the cot i = 1.4, resulting in a slope angle (i) of approximately 35°. Therefore, the actual safety factor is well in excess of 1.5, since the actual slope angle is much less than the slope angle necessary to attain a safety factor of 1.5. The temporary stockpile located on the west side of the final cut of Pit 2 will contain approximately 460,000 cy of overburden. The stockpile will be built in lifts by truck and dozer, thereby assuring adequate compaction. The physical dimensions of the stock- pile are as follows: Length 700 ft Width 300 ft Height 75 ft Side Slopes 1V to 1H The stockpile will be inspected on a regular basis for stab- ility, erosion and sediment control, thereby enabling corrective action be taken before a serious problem develops. It is conceivable that if any further mining north of the permit area takes place, the overburden stockpile will be placed nearer the proposed final cut rather than in the position indicated on Figure 2A. Any such change will be done only after appropriate permit modifications have been approved. -10-