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i• <br />TABLE III.4 <br />MINIMUM FACTOR OF SAFETY AGAINST PILLAR FAILURE <br />l J <br />MINING <br />METHOD LOCATION DEPTH {FT) PILLAR <br />HEIGHT <br />(FT) LOAD <br />TRANSFER <br />DISTANCE <br />(FT) MIN. <br />FACTOR OF <br />SAFETY` APPROX. <br />PILLAR <br />SIZE <br />ROOM & <br />PILLAR RP1 400 7.5 N/A 3.19 <br /> RP2 400 8.0 N/A 3.50 <br />LONGWALL LW1/LW2 600 8.4 148 1.76 80x100 <br /> LW2ILW3 700 6.3 171 1.58 80x100 <br /> LW3/LW4 850 8.5 204 1.37 80x100 <br /> LW4/LW5 950 8.7 226 1.27 80x100 <br /> LW5/LW6 1000 8.8 236 1.22 80x100 <br /> LW6/LW7 1150 9.1 266 1.22 85x100 <br /> LW7/LW8 1250 8.8 285 1.21 95x120 <br /> LW8/LW9 1345 8.5 302 1.22 97x120 <br />`Assumes angle of internal friction (m) of 38.5° and pillar edge strength of 560 psi. <br />III.A.7.g Subsidence Prevention. BME utilizes a mining system that includes a subsidence control <br />plan that will minimize damage and lessening value and use of the surface lands. The measures used <br />in the mine to reduce the likelihood of subsidence damage besides longwall mining and full pillar <br />extraction include the following: <br />1) Permanent entryways - A network of mains and submains consisting of multiple entries are <br />driven to outline the coal deposit (Map 119). These entries, which consist of 4 to 6 openings, <br />are developed on 80-foot centers. They will be permanently supported to withstand caving for <br />the life of the mine. <br />• ~Chi;4ta ~ ~ ~ RG^rn't~w~ (S. ~'t'1?2) ~Y-~ <br />