Rock Bolting at the Room and Pillar Method at Great Depths

Abstract

A part of the coal reserves in the Karvina subbasin of the Upper Silesian Coal Basin is situated in protection pillars that lie under built-up areas. The longwall mining method is not suitable in these areas because significant deformation of the surface is not allowed. The room and pillar method with stable coal pillars has been proposed to minimise strata convergence. The method has been examined within the shaft protective pillar located in CSM-North Mine coal seam No. 30, where the mining depth ranged from 700 to 900 meters, being perhaps the deepest room and pillar panel in coal mining in the world [1–5].As there is no relevant experience of using this method in the Upper Silesian Coal Basin, an extensive monitoring system has been implemented to enable the mining trial to continue safely. The monitoring is focused on the load-bearing capacity of the coal pillars and strata deformation changes induced by the room and pillar mining method. Precise monitoring was carried out in two adjacent coal pillars located within the row of pillars forming the panel. To monitor roof deformation, fourteen pairs of 5-level multipoint extensometers monitored roof displacements and eleven strain-gauged rockbolts were installed at various locations. Seven hydraulic dynamometer load cells measured the cable bolt loads were installed at the roadway intersections around the monitored pillars.The integral constituent of the extraction method (using driving machines like the Bolter Miner) is bolting as the sole support system of the roadways. The contribution deals with the behaviour of roof bolting, including the loading of the bolts, yielding of the rock mass and convergence in the roadways. The monitored parameters’ database used to measure whether the room and pillar method is successful at this depth forms a necessary condition for verification of this method and its future application in conditions experienced in Upper Silesian Coal Basin.