Laserfiche WebLink
"D" Seam Longwall Subsidence Page 1 August 17, 1998 <br />EXECUTIVE SUMMARY <br />Plate 1 through Plate 5 present worst-case predictions of <br />vertical surface subsidence over the panel groups and Plates 6 <br />through 10 present the maximum tensile and compressive strain <br />locations over the panel groups for the planned Sanborn Creek Mine <br />"D" Seam longwall mining, shown on Plate 11. The scale of these <br />worst-case subsidence prediction plates is 1-inch equals 1000 feet. <br />The predicted vertical subsidence will probably exceed the actual <br />vertical subsidence by approximately one-third because of various <br />conservative assumptions applied. The most conservative assumption <br />was that the full thickness of the "D" Seam, indicated by the <br />drilling program, will be extracted wherever present. The <br />indicated seam thickness varies from 7 feet to 17 feet. It is <br />unlikely that one set of longwall equipment will be able to fully <br />extract both the minimum and maximum seam thicknesses. The panel <br />group subsidence predictions also conservatively assume that all <br />longwall panels in the group are instantaneously extracted. The <br />collapsed roof rock, accompanying actual sequential panel <br />extraction, will progressively provide overburden support. The <br />expansion of the collapsed roof rock will prevent the maximum <br />possible predicted subsidence from developing when the gateroad <br />pillars crush out as planned. <br />Trough subsidence above and adjacent to the planned Sanborn <br />Creek Mine "D" Seam longwall panels is the only type of subsidence <br />that can affect either the ground surface or mine workings in the <br />underlying "B2" Seam, "C2" Seam and Blue Ribbon Mine "B" Seam, <br />shown on Plate 11. Chimney subsidence is unlikely to develop <br />through the minimum 290 feet of overburden to the ground surface <br />over the longwall panels or adjacent supported gateroads. Maximum <br />trough subsidence at the surface overlying and adjacent to the <br />planned longwall panels in the "D" Seam, indicated on Figure 1, <br />will result from longwall mining groups of three adjacent longwall <br />panels and from crushing of the gateroad pillars between the <br />individual panels. Maximum subsidence will occur following mining <br />of the third panel and approach the predicted subsidence at the <br />time the last of the gateroad yield pillars between the second and <br />third longwall panels in the group of three panels crush under the <br />loads arched from over the adjacent mined out longwall panels. <br />Subsidence extending over one group of three longwall panels from <br />mining the adjacent groups of three longwall panels will be minimal <br />because panel groups will be isolated by approximately 280-ft wide <br />barrier pillars. <br />Individual <br />starter rooms at <br />at the equipment <br />• Planned width of <br />Panels #1 - #12) <br />#16) . <br />panel depths range from a maximum of 2550-ft at the <br />the north end of Panel #2 and Panel #4, to 290-ft <br />recovery room at the south end of Panel #7. <br />panel groups is 2220-ft (Panel groups containing <br />to 2960-ft (Panel group containing Panels #13 - <br />1 <br />