Laserfiche WebLink
<br />Vertical Stress from overburden density (Sv): <br />(for maximum depth of 1700 ft. for main entry pillars in life of mine.) <br />Sv = 150 pcf x 1700 ft. x (lft2/144in2) <br />= 1771 psi <br />Maximum Stable Vertical Pillar Stress (Sv): <br />Sv = Sv (tan S) + C <br />= 1771 (3.95) + 1170 = 8165 psi <br />Width of failed region at edge of pillar (Y): <br />Y = m ,. <br />tans In Sv <br />C <br />where m = 10 feet of pillar height <br />~ J <br /> <br />Y = <br />10 ft <br />8165 <br />= 3.3 ft. = 3.5 feet <br />3.95 In <br />Therefore, the total failed (unsupporting) region in any one direction of <br />pillar is 7 feet. The confined central core will therefore be intact, and the <br />pillar strength can be estimated on the assumption that it is a wide pillar <br />(ref. 3). <br />Assume the intact confined central core of 53 feet x 74 feet supports a <br />maximum of 8165 psi. In the worst case with no pressure arch, the pillar <br />]oading is estimated from the Tributary Area Theory, (see Figure C). <br />Load Carrying Capacity of Pillar: <br />C.C. = Confined Core 53 ft x 13 ft = 3869 ft2 <br />T.A. = Triburaty Area 80 ft x 100 ft = 8000 ft2 <br />Spa = Pillar average stress <br />= Sv(C.C.) = 1771 psi ($869) = 3662 psi <br />Factor of Safety: <br />Max. Pillar Stress __ 8165 __ <br />F.S. = Avg. Pillar Stress 3662 2.2 <br />Ex. 7-3 <br />