Laserfiche WebLink
' • Case 2 - maximum cover of 1000 feet. <br />mining height = 5.5 feet <br />width of excavation = 350 feet <br />width = 350 = .35 <br />depth 1000 <br />From chart, subsidence ratio = .28 <br />maximum subsidence = .28 x 5.5 feet <br />= 1.54 feet <br />Case 3 - average cover of 500 feet. <br />mining height = 5.5 feet <br />width of excavation = 350 feet <br />width = 350 = 0.70 <br />depth 500 <br />• From chart, subsidence ratio = .63 <br />maximum subsidence = .63 x 5.5 feet <br />= 3.46 feet <br />Assuming that both seams would be fully extracted at the same <br />location, the above numbers would be approximately doubled. <br />As the initial panel in an area is retreated, subsidence will <br />occur in a bowl-shaped configuration with maximum subsidence <br />occurring directly over the middle of the panel. As each <br />adjacent panel is mined, the barrier pillar between each will <br />be extracted, thus effecting uniform maximum subsidence over <br />wide area, as if the bottom of the bowl was being extended. <br /> <br />r ~ <br />L_J <br />56$ <br />D. H. EMLING COMPANY <br />