Dynamic disaster control under a massive igneous sill by grouting from surface boreholes

An overlying 140-m-thick massive igneous sill has adversely affected mining activities considerably in the Haizi Coal Mine, China. A coal and gas outburst disaster occurred during the drivage for a subsequent longwall, after the extraction of two faces in the II102 mining area. The massive sill was determined to be primarily responsible for this outburst owing to the bed separation that occurred below the sill due to the sill׳s large span. This is because such separation meant the massive sill was not supported by the gob, as in a general case, but it was supported by the solid coal instead, resulting in a long load transfer distance that caused the drivage gate to collapse unexpectedly into the abutment. Thus, it was determined that the high abutment pressure primarily triggered the outburst. Such disaster risk would have remained had the drivage in the gate continued, and a wide-area and sudden roof fall could have occurred during the extraction of the next longwall had the igneous sill broken suddenly as the critical span was reached. With these risks in mind, a field trial of a method of grouting into the overburden of the abandoned faces from surface boreholes was conducted for dynamic disaster control. This technique alleviates the abutment pressures and restrains the igneous sill deflection by eliminating fractures and voids in the overburden using grouting. The adoption of this grouting method led to the subsequent drivage and mining of a further 510 m without occurrence of any further dynamic disasters.