2001-12-11_PERMIT FILE - C1980007A (2)

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April 1989 • RESTJLTS-EXPAREA AI•IALYSIS The area covered by this analysis for both longwall and room-and- pillar muting ittclttded a portion of three panels and bleeders. As att example, Ei.gures 3.4.A.5 and 3.4.A.6 show 'the layouts and associated stress distributions for longwall attd room-and-pillar mining itt Area III. There is a plane of symmetry on the bottom and right vertical margins so that only Otte q[tarter of the area modeled is shown. In Figure 3.4.A.5 the left longwall is completed attd the gate ott the middle longwall is about 200 feet behind. A face length of 700 feet and two-entry gate road system with yield pillars was used in the design. In room-and-pillar mining (Figure 3.4.A.6), the first panel, beside a solid block of coal, is completed. In tite second panel, the 1st pillar of the second row is being mined attd stresses are being transferred to the first row of pillars. Itt the white areas itt both figures, vertical stresses are below 250 psi. These areas represent open rooms, the face, and caved areas itt the gob. Cross-sections were taken in four areas for CI[e longwall and itt two areas for room-attcl-pillar mining, as shown i.tt Figure 3.4.A.5 and 3.4.A.6, for detailed evaluation of stress profiles. Stress transmitted to the upper seam (E) due to mining in the B Seam was calculated in the same way. •• The geotecltnical design is shown in Tables 3.4.A.15.1 to 3.4.A.24 in terms of pil.l.ar sizes attd safety factors. Room spans in all cases were ?~ feet. Mining ![eights were 7 ft £or tl,e F Seam and 12 ft for the F. and B Seams. RESULTS-MILdAP ADIALYSIS In multi-seam mining, it is very important t.o evaluate how mining impacts tLe stability of he interburden and adjacent seams. In tlti.s study, this was accomplished by the MICIAP analysis. Results are presented graphically in terms of safety factor contours. Two cottditiotts Caere evaluated: a mined out, no cat~i.ng condition which occurs I~efnre a cave is established, and a good cave condition. F.xperiettc? itt the F Seam indicated good to excellent caving conditions. An etcample of the first case is illt[str.ated in Figure 3. 4. A.7 where t}[P safety factor distribution caused by B Seam mittittg i.tt Area ICI is shown. Safety factor areas of 1.0 or less reflect. movements/failure along preexisting joints. Thus, in this case, both the E and F Seams are affected. Figure 3.4.A.8 shows the second cottdi.tion, i.e., the safety factor fir the same area afi ~r a good, tight cave is developed in the R Seam. Safety factor areas of 1 nt' less decreased significattt-ly an~i ttte E and E Seams are unaffected. Itt practice, i.tt-situ conditions often lie between these two Pxtremes. Good mine planning and design will be critical to ensure that a tight cave develops before commencing upper or lower seam mining. •