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Pillar Analysis -Tributary Area Method <br />• <br /> <br />Ref: "Coal Mine Ground Control", Peng, pp 175-6 <br />"Rock Mechanics and the Design of Structures in Rock;'Obert and Duval, p. 540 <br />Drawing No. E8-3362 shows overburden contours of about 500 feet in the Hubbard <br />Creek -Sunflower Energy Facilities area. A 500 foot overburden thickness is a <br />prudent assumption as overburden depth ranges as low as 165 feet in this area. <br />~- -----~ <br />I I <br />~ 90~ 1 <br />~ 20 <br />I ~ <br />oo' <br />i <br />i ~ <br />Influencing area: (90')(100') = 9000 ftZ <br />Pillar area: (90'-20')(100'-20') = 5600 ft2 <br />Assuming 160#/ft3 overburden: <br />Pillar stress = (9000 ftZ)(500 ft)(160#/ft3) = 892. 9 psi <br />(5600 ft) (144 in /ft~ <br />Ten coal samples were taken from the Somerset Mine in 1977 and tested for their <br />complessive strength. The following is a summary of those results: <br />Ref: Peng, P. 188 <br />Obert and Duval, P. 332 <br />Co = C Where Co =Comp. strength fora 1:1 <br />0. 778 + 0. 2Z2(L length/dia. ratio <br />Cp =Comp. strength of a sample <br />where 2>L/D>1/3 <br />• F-47 <br />Rev. 1: 6-18-81 <br />