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<br />-z- <br />• area supported, the maximum load supported is <br />Correction factor = Area of Pillar = 130 ft X 60 ft <br />Area to be supported 150 ft X 80 ft=0.6` <br />by each pillar <br />Maximum Load = 550 ft X l.lpsi per ft = 931 psi <br />.65 <br />'!~re~,c_t~ngof the..e.ntry pilJ~ars, is galculaEedMus g,,,;,,~h <br />- ~~ ~ - o;rmula ~ <br />S = K~ <br />T <br />where S = strength of pillar in psi, W = least pillar width, <br />T = pillar thickness (heighth mined) and K = the crushing <br />strength of coal to psi. <br />A study by John T. Boyd Company in 1977 established <br />the compression strength of G-seam coal to be between 2,777 psi <br />and 3,970 psi. In order to maintain the worse case scenario, <br />the 2,777 psi will be used. Therefore, W = 60 ft., T = 10 ft., <br />and K = 2,777 psi. <br />S = 2,777 psi X 10 ft. = 6,802 psi. <br />• The Factor of Safety is <br />, x <br />~:,is.M = 9~i psi = Jr•:3:.~ <br />In the Morrison-Corl~tt-Rice formula, a factor of safety of <br />4 to 5 is suggested. Thus, the pillars have a factor of <br />safety on a worse case basis. <br />The entry pillars adjacent to the east and west edge of the <br />protected area are the standard 80 ft. by 60 ft. pillars <br />developed on 100 ft, by 80 ft. centers. These adjacent pillars <br />support an overburden of 600 feet. llsing the Morrison-Co rlett- <br />Rice formula, the factor of safety is calculated to be 6.8, <br />still well above the suggested factor of safety. <br />The required width of the barrier pillar between <br />1st and 2nd East Section4s is calculated using the Ashley, or <br />Mine Inspectors Formula. <br />-SME Mining Engineering Handbook, <br />3SME Mining Engineering Handbook, <br />• 4SME Mining Engineering Handbook, <br />Vol. 1, Pg. 13-104 <br />Vol. 1, Pg. 13-104 <br />Vol. 1, Pg. 13-105 <br />