Ground motion characteristics and their cumulative impacts to burst risks in underground coal mines

Ground motions resulting from seismic waves are one of the main factors to trigger coal burst hazards in underground mines. Ground motion induced dynamic impacts may apply to the highly stressed coal/rock mass and initiate dynamic failure. Although ground motion analysis has been widely used in burst-prone hard rock mines for designing support systems, there are only few studies focusing on the understanding ground motion characteristics in coal mines and their relationship with the coal burst damage. Therefore, based on nine-months seismic monitoring in a case study coal mine, this paper conducted a thorough analysis on quantifying ground motions to roadways in both far-field and near-field zones and correlating strong ground motions to actual coal burst damage. The results showed that most far-field ground motions were insignificant, which were less likely to initiate coal burst damage. However, with the same energy levels and hypocentral distances, the seismic events in coal mines can produce higher far-field ground motions than those in hard rock mines. Compared with the far-field ground motions, the near-field ground motions had much higher intensities. The strong dynamic impacts induced by the near-field ground motions may trigger dynamic failure in coal or rock mass when it is already critically stressed. An index called the number of high ground motions (NHGM) was developed to link ground motions with burst risks in roadways. The roadway zone that had experienced a long history of intensive ground motions, indicated by a higher degree of NHGM, were more likely to expect coal bursts in the future.