PERMFILE104696 - Laserfiche WebLink

Home Browse Search

Sanborn Creek Subsidence Page 15 September 2, 1997 LONGWALL PANEL TROUGH SUBSIDENCE PREDICTION • It was necessary to calculate vertical subsidence from longwall mining individual panels before proceeding with prediction of panel group subsidence. These predictions were made using the NCB (1975) "Subsidence Engineers' Handbook", which was developed from 167 case histories of subsidence monitoring. The Handbook ;, states, - "Prediction of subsidence by the above method should be correct to 108 in the great majority of cases." Individual panel subsidence prediction probably represents the most accurate part of longwall subsidence prediction. However, the prediction method is for independent isolated panels. Multi-panel layouts are simply treated as wider panels by the NCB method. The use of single entry gateroads at the full mining height in Great Britain eliminates the gateroad pillar subsidence effect. This would be unrealistic for the planned panel groups because of the 8.5-ft high three-entry gateroads, the 50-ft and 30-ft wide i_ gateroad pillars and the 12-ft longwall panel mining height. Table 9 presents the predicted worst-case subsidence _ predictions for each of the individual 12-ft high planned longwall panels shown on Figure 1. Subsidence predictions were made for panel profiles perpendicular to the center of the panel starter room face, at each panel ribside at a distance of one-half the '~ planned panel width inside the panel from the starter room, at the ribside location of each depth contour shown on Figure 1, at the center of the recovery room and at each panel ribside at a distance of one-half the planned panel width inside the panel from the fI recovery room. L~ As indicated on Table 9, subsidence profile input data included whether the subsidence prediction should be reduced ~ because parts of the overlying ground had not previously been ,_ subsided by mining in the Oliver No. 1 Mine or the Hawksnest Mine. The NCB (1975) "Subsidence Engineers' Handbook" states, C "When considering workings with any w/h value in a virgin area the prediction from Fig. 3 (which was derived from ~ cases of multi-seam workings) should be reduced by a multiplying factor of 0.9." The predicted maximum vertical subsidence (Sm,,,) of the ground [- surface was obtained along each of the profile locations described above for an individual panel by multiplying the 12-ft longwall mining height by the panel width/depth correction factor. The panel width/depth correction factor graph is included in Appendix L~ 15