Strata Behaviors and Rock Burst-Inducing Mechanism under the Coupling Effect of a Hard, Thick Stratum and a Normal Fault

The study of strata behaviors of hard, thick stratum (HTS) and faults in underground coal mines is significant to understanding and predicting the mechanism of rock bursts. By considering the occurrence of a HTS and a normal fault (NF), the strata behaviors and rock burst-inducing mechanism were studied using the universal distinct element code (UDEC) numerical simulation and field observation. The results show that prior to failure, a HTS continues to suspend and the lower strata breaks and moves easily because of fault cutting and fault activation. This process induces microseismic events accompanied by the release of a small amount of energy that concentrates near the fault and beneath the HTS. However, the mining stress concentrates and strain energy accumulates in the surrounding rocks because of the large-scale suspension of the HTS, thereby providing sufficient energy for rock bursts to occur. When the HTS suspension increases to the ultimate span, the HTS breaks and slips along the fault plane. Moreover, the fault-plane stress varies notably and the fault slipping is clear. These conditions indicate that the fault activates and destabilizes violently. A large amount of strain energy is released because of the HTS failure and fault slipping, easily inducing violent rock bursts. Hence, the mechanism that induces rock bursts can be divided into two stages: the accumulation of strain energy prior to HTS failure and the release of strain energy because of the coupling effect of HTS failure and fault slipping. In particular, more attention should be paid to the latter stage.