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<br /> <br /> <br />Project: New Castle MSHA Permit Date: 900820 Page: 1 <br />Subject: Barrier Pillar Design By: AB Pile: 1145-C <br />' Computation: <br /> The barrier pillar will be made out of coal that is expected to be <br />' able to withstand the pressure of the disposed materials in the <br /> room. The analysis makes the following assumptions: <br /> 1. The pillar is subject to the full static pressure of the <br />' backfill, assuming that it the backfill has no shear strength. <br /> 2. The pillar resists failure by frictional shear along its <br />' contacts with the remaining coal (~ = 20°), the hangingwall <br />° <br />° <br /> ), and the footwall rock (~ = 15 <br />). The <br />rock (~ = 15 <br /> coal/rock contacts assume a clay layer. <br />' 3 The backfill densit <br />is 100 lb/cu <br />ft <br /> . . <br />. <br />y <br /> 4. The maximum elevation that the slurry could achieve is 6250 <br />' feet; the elevation of the base of the bulkhead is 5950 feet. <br /> 5. The pillar is 50 feet wide and 150 feet high (along the seam), <br />' and it is 120 feet thick. <br /> 6. The stress conditions in the mining area are assumed to be <br /> lithostatic, with the rock density being 140 lb/cuft, and the <br />' average overburden height equal to 500 feet. <br />' The driving force on the barrier pillar is: <br />= 50 ft * 150 ft * (6250 ft - 5950 ft) * 100 lbf/cuft <br />F <br /> p <br />FD = 2.25 x 108 lbf = 112,500 tons <br />' The average stress on the pillar contacts is: <br /> ap = 500 ft * 140 lbf/cuft = 70,000 lbf/sgft = 35 tsf <br /> The resistive force on the edges of the pillar of 120 feet width <br />' is: <br /> FR = 35 t * 2 * [50 ft * 120 ft * tan 20° <br /> + 150 ft * 120 ft * tan 15°] <br />' FR = 490,000 tons <br /> The factor of safety against sliding using these conservative <br /> para meters is: <br />' FS = 490,000 / 112,500 tons = 4.~ <br />1 <br />1 <br />Adrian Broxn Consultants, Inc <br /> <br />