Laserfiche WebLink
Sanborn Creek Subsidence Page 24 September 2, 1997 <br />is 8.09-ft. This results primarily from the crushing of the <br />gateroad yield pillars. Mining of Panel #3 makes a smaller <br />contribution to predicted worst-case subsidence of the ground <br />surface over Panel #2. <br />r LONGWALL PRNEL GROUP SUBSIDENCE PREDICTION <br />The maximum surface subsidence predicted from longwall mining <br />- 12-ft of coal in Panel #2 and Panel #3 is more than would result <br />from longwall mining the individual panels. Table 5 presents the <br />calculated worst-case surface subsidence and strains resulting from <br />,_ applying the NCB method using the assumption that a panel 1300-ft <br />wide by 2520-ft long is longwall mined at the location of Panel #2 <br />~- and Panel #3. Such a panel matches the outer boundaries of Panel <br />#2 and Panel #3 without any intervening gateroad pillars. The <br />maximum predicted vertical subsidence in this case is 8.77-ft <br />compared to an individual panel subsidence prediction of 3.90-ft <br />for Panel #2 by itself and 5.19-ft for Panel #3 by itself. Table 5 <br />presents the maximum subsidence prediction for the same assumption <br />_ applied to all three panels in the first panel group longwall mined <br />as a single 1900-ft wide panel, without any gateroad yield pillars. <br />!' The maximum predicted vertical subsidence increases to 9.62-ft for <br />~ Panel #2, Panel #3 and Panel #9 mined as a single longwall panel, <br />~_ <br />without gateroad yield pillars. <br />The assumption of no gateroad yield pillars is unrealistic, <br />particularly for the 8.5-ft high gateroads and 12-ft high panels. <br />Therefore, the room and pillar subsidence prediction method <br />L presented by Abel and Lee (1989) was used to estimate the <br />subsidence resulting from crushing of the intervening gateroad <br />yield pillars. Table 6 presents the results of the predictive <br />~ analysis. The planned gateroad pillars are 100-ft long on 120-ft <br />•.- centers. One row of pillars is 50-ft wide and the other 30-ft <br />wide. The critical pillar, i.e. the pillar that will flatten the <br />least under the load transferred to the gateroad pillars, is the <br />wider 50-ft pillar. Table 6 presents the average tributary <br />gateroad pillar stress. The actual pillar stress on the 50-ft wide <br />C pillar will be somewhat higher immediately before failure because <br />the narrower 30-ft pillar should crush first, shedding its load to <br />the wider gateroad pillar. The magnitude of vertical gateroad <br />pillar stress will crush the gateroad pillars when the second <br />L adjacent panel is mined past. <br />L <br />~M <br />24 <br />