PERMFILE45400 - Laserfiche WebLink

Home Browse Search

"D" Seam Longwall Subsidence Page 22 August 17, 1998 • INDIVIDUAL LONGWALL PANEL TROUGH SUBSIDENCE PREDICTION It was necessary to calculate vertical subsidence for individual longwall mining panels before proceeding with prediction of panel group subsidence. Ultimate subsidence toward the center of a panel group will exceed subsidence for an individual panel because of the planned crushing of the gateroad pillars after the adjacent panels have been retreated. Ultimate subsidence at the ends of an individual panel in a panel group will exceed subsidence at the ends of the individual panel alone because the effective width of the panel group exceeds the width of the individual panel. The predictions of individual panel subsidence, necessary to begin calculating panel group subsidence, were made using the NCB (1975) "Subsidence Engineers' Handbook", which was developed from 187 case histories of longwall panel subsidence monitoring. The Handbook states, "Prediction of subsidence by the above method should be correct to 10$ 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-fit high three-entry gateroads, the 50-ft and 30-ft wide gateroad pillars and the variable "D" Seam longwall panel mining heights indicated in Table 3. Table 5 presents the predicted worst-case, maximum, vertical ground surface subsidence and maximum horizontal tensile and compressive strains for each of the individual planned longwall panels shown on Figure 1. These initial worst-case subsidence predictions were estimated assuming no additional subsidence from previous and subsequent longwall mining of the adjacent panels. Maximum single panel surface subsidence and strain predictions were made for vertical panel cross sections in planes perpendicular to the center of the panel starter room face, perpendicular to the panel ribsides at the intersection of each depth contour shown on Figure 1 and perpendicular to the center of the recovery room. As indicated on Table 5, subsidence input data included whether the subsidence prediction should be reduced because parts of the overlying ground had not previously been subsided by room and pillar mining in the underlying "C" Seam and "B" Seam. The NCB (1975) "Subsidence Engineers' Handbook" states, 2z