Laserfiche WebLink
• dicted maximum tensile strain at 1200-ft depth will increase from 2500 <br />over the first panel to 3510 over that and all other longwall panels in that <br />series when the second panel is extracted. Table 1 presents the "worst-case" <br />longwall subsidence predictions at selected depths, and Figure 3, 4 and 5 pre- <br />sent this data graphically. <br />~B~e~ ,on a e ~pr`.e'di`c'trio'fis*Yfior~mu~tsvpd~e~a~d5~a'c"e'fi°t"'Zrongwal~l'"lia~hveIl~+~'su~bsid~ence <br />assume an infinite panel width. This is conservative because it eliminates the <br />subsidence reduction resulting from failed gateroad pillars partially supporting <br />the overlying strata. In effect, it has been assumed that the gateroad pillars <br />have been fully extracted. <br />It has been assumed that there has been no previous mining and subsidence in <br />• the area of the Colorado Ute power line, i.e. virgin ground conditions. As <br />stated by the NCB (1980, p. 10), "When considering workings of any w/h", (panel <br />width to depth ratio), "value in a virgin area the prediction...should be reduced <br />by a multiplying factor of 0.9." The calculations for the case of previous multiple <br />seam mining and subsidence have been performed and are presented in Table 2. The <br />Appendix contains the worked example for calculation of the maximum strain prediction. <br />The room and pillar mining panels are planned to be 520 ft wide. Pillars <br />are to be left in the panels to prevent subsidence. However, the "worst-case" <br />subsidence prediction was made assuming these 15-ft wide by 80-ft long retreat <br />pillars crush. The planned percent panel extraction is 76%. The "worst-case" pre- <br />dicted maximum compressive strain occurs over the center of each panel since each <br />. panel is planned to have rigid boundary (barrier) pillars. However, the <br />