Trial of small gateroad pillar in top coal caving longwall mining of large mining height

Coal seams in Tashan Mine of Datong Coal Group in China average 15 m thick and have been mined by the top coal caving longwall mining method of large mining height. Mining height was 3.8 m and the top coal caving height was 11.2 m. The gateroad pillar between panels was 38 m. During retreat mining, serious bumps occurred in the gateroads on both sides of the pillar affecting safety production. Therefore, pillarless mining was experimented. Using numerical modeling and comparative study of cases of similar mining condition, it was decided to employ a 6 m wide pillar, rather than the previous 38 m wide pillar. Support system for the gateroads was designed and implemented. During gateroad development, pillar failure conditions and entry deformation were monitored. Hydraulic fracturing method was employed to cut off the K3 sandstone along the entry rib so as to reduce the abutment pressure induced during retreat mining. Support reinforcement method combining grouting and advanced reinforcement methods was proposed to insure stable gateroad ahead of mining. Methane drainage and nitrogen injection were implemented to eliminate hazards associated with mine fire and spontaneous combustion. Since the development of gateroad has just completed, and retreat mining has not begun, the effectiveness of the proposed methods is unknown at this point. However, monitoring will continue until after mining. The results will be published in a separate paper.