Mechanism and risk assessment of overall-instability-induced rockbursts in deep island longwall panels

An increasing number of mines in China are being subjected to overall-instability-induced (OII) rockbursts in extracting deep remnant island longwall panels, causing severe damage at far larger scale and intensity compared with common local rockbursts. Using the island longwall panel LW1305 at Zhaolou Coal Mine as a case example, this paper investigates the mechanism of the newly defined OII rockburst by means of stress and microseismic monitoring, and then proposes a straightforward risk assessment method for OII rockbursts based on the actual bearing index in an attempt to provide guidelines for making engineering judgement. The proposed risk assessment method was successfully applied to LW1305, and the assessment result is supported by the occurrence of an OII rockburst in LW1305, and further verified by numerical modeling and microseismic monitoring.