Coal burst and mining-induced stress evolution in a deep isolated main entry area – A case study

Abstract

Main entries in some underground coal mines are tunneled into coal seams. During coal mining, main entries usually have a one-side gob or two-side gobs. Serious coal bursts have occurred in the isolated main entry area (IMEA). In this study, coal bursts in the IMEA are investigated. A large-scale numerical model is built to depict the static-dynamic stress evolution in the IMEA. Likewise, the study discusses the coal burst mechanism in the IMEA and proposes the measures to decrease the coal burst risk. During tunnelling of the main entry, coal bursts in the IMEA occur in the intersection of roadways. During coal mining, coal bursts mainly arise in the area between the gobs on both sides. Coal bursts in the IMEA are induced by high static and low dynamic stress. When coal is mined, the abutment stress around the gobs on both sides transfers to deeper regions and intersects in the IMEA, leading to higher static stress in coal mass. The seismic-based dynamic stress negatively correlates to the distance between the seismic sources and the IMEA. During coal mining, dynamic stress fluctuates, then the amplitude decreases and finally remains at a low value and exerts slight dynamic disturbance on the IMEA. When static stress is low, only higher dynamic stress can lead to coal bursts. However, when static stress is high, low dynamic stress can induce coal bursts. Coal bursts in the IMEA are caused by the superposition of high static stress in coal seam and low seismic-based dynamic stress disturbance from longwall panels. Roof blasting in the IMEA and roof pre-splitting blasting in longwall panels are proposed and implemented on site. Field monitoring results indicate that the de-stressing measures significantly decrease the coal burst risk in the IMEA.