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I• <br />l J <br />TABLE 111-4 <br />MINIMUM FACTOR OF SAFETY AGAINST PILLAR FAILURE <br />MINING <br />METHOD <br />LOCATION <br />DEPTH (FT) <br />PILLAR <br />HEIGHT <br />(FT) <br />LOAD <br />TRANSFER <br />DISTANCE <br />(FT) <br />MIN. <br />FACTOR OF <br />SAFETY` <br />APPROX. <br />PILLAR <br />SIZE <br />ROOM & <br />PILLAR <br />RP1 <br />400 <br />7.5 <br />N/A <br />3.19 <br />RP2 <br />400 <br />8.0 <br />N/A <br />3.50 <br />LONGWALL <br />LW1 /LW2 <br />600 <br />8.4 <br />148 <br />1.76 <br />80x100 <br />LW2/LW3 <br />700 <br />8.3 <br />171 <br />1.58 <br />80x100 <br />LW3 /LW4 <br />850 <br />8.5 <br />204 <br />1.37 <br />80x100 <br />LW4 /LW5 <br />950 <br />8.7 <br />226 <br />1.27 <br />80x100 <br />LW5 /LW6 <br />1000 <br />8.8 <br />236 <br />1.22 <br />80x100 <br />LW6 /LW7 <br />1150 <br />9.1 <br />266 <br />1.22 <br />85x100 <br />LW7 /LW8 <br />1250 <br />8.8 <br />285 <br />1.21 <br />95x120 <br />LW8 /LW9 <br />1345 <br />8.5 <br />302 <br />1.22 <br />97x120 <br />`Assumes angle of internal friction (m) of 38.50 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 />• iWItla � � ReiA-o, &,1416102) Y- <br />