Rock bursts have recently become a serious problem in the horizontal section mining of steeply inclined extra-thick coal seams (SIETCSs). However, few studies have been carried out to investigate their mechanisms and prevention. In this study, numerical simulation and field measurements were carried out to investigate the mechanism of rock bursts in the horizontal section mining of an SIETCS. A Universal Distinct Element Code (UDEC) Trigon model was built, based on the Yaojie No.3 Coal Mine, and calibrated through laboratory tests and RQD methods. The results demonstrate that the coal in the elastic zone around the roof is in a high static stress state, due to the asymmetric clamping and squeezing of the roof and floor. Strong dynamic loads are formed by breakage of the roof and the failure of multiple hinged beam structures during the evolution process of the overlying strata. Rock bursts occur on the roof side when the superimposition of the static stress ${\sigma }_s$ and stress increment ${\sigma }_d$ induced by such dynamic loads is greater than the critical stress ${\sigma }_{\min }$ of the coal and rock. We propose a technical prevention scheme for the considered mine. Field studies suggest that the proposed technology can effectively prevent and control rock bursts in the horizontal section mining of SIETCSs.

Coal bursts caused by mining-induced seismicity occur in the working face in steeply inclined and extra thick coal seams (SIETCSs). This article presents a case study in SIETCS through discrete element simulation as well as field investigation. The evolution of the coal burst was studied from the perspective of stress distribution, crack propagation and coal fragment ejection. The results showed that dynamic failure mainly occurred in the coal near the roof. The deep bottom coal and the top coal near the roof are under high static stress due to the clamping effect of the roof and floor and the rotation of the deep roof. The coal burst in the working face was triggered by mining-induced seismicity. The coal burst occurred when the sum of the static stress and the dynamic stress caused by the mining-induced seismicity exceeds the sum of the ultimate strength of the coal and the support strength, which was called the ‘clamping-rotation-dynamic loads’ mechanism. During the coal burst, the cracks developed rapidly into the deep bottom coal and the top coal on the roof side. The results can serve as an important reference for the coal burst failure mechanism in the working face in SIETCSs.

Monitoring and early-warning are critical for the prevention and controlling of rock burst in deep coal mining. In this study, rock burst risk assessment criterion was built based on the correlativity between seismic velocity and stress state in coal and rock body. Passive seismic velocity tomography using mining-induced seismic waves was conducted regularly and continuously. The evolution of rock burst risk and range in front of a deep longwall panel with folds and adjoining goaf was determined. The influence of pressure-relief measures on rock burst risk was analyzed. The study results indicate that burst risk level and range during panel retreating increase first and then decrease, the peak is reached when it is located at 1# syncline shaft area. When approaching the crossheading, high burst risk zones distribute along the crossheading and further intersect with those in 1# syncline shaft area. Burst risk zones in the inclination of panel show distinct zoning features. Tomography results are in good agreement with the drilling bit result, rock burst occurrence, microseismic activity, and working resistance of hydraulic supports. Pressure-relief measures and mining layout have a distinct influence on burst risk of longwall panel. For prevention and controlling of rock burst risk in deep coal mining, pressure-relief measures should be optimized based on passive tomography results.

Discrimination of various microseismic (MS) events induced by blasting and mining in coal mines is significant for the evaluation and forecasting of rock bursts. In this paper, multifractal and moment tensor inversion methods were used to investigate the waveform characteristics and focal mechanisms of different MS events in a more quantitative way. The multifractal spectrum calculation results indicate that the three types of MS waveform have different distribution ranges in the multifractal parameters of ∆α and Δf(α). The results show that the blasting schemes also have a great influence on MS waveform characteristics. Consequently, the multifractal parameters of ∆α and Δf(α) can be used to discriminate different MS events. Further, the focal mechanisms of MS events were calculated by seismic moment tensor inversion. The results show that an explosion is not the dominant mechanism of deep-hole blasting MS events, and the CLVD and DC components account for an important proportion, indicating that some additional processes occur during blasting. Moreover, the coal-rock fracture MS events are characterized by compression implosion or compression/shear implosion mixed focal mechanisms, while the overburden movement MS events are tensile explosion or tensile/shear explosion mixed focal mechanisms. The focal mechanisms and nodal plane parameters have close relationships with the inducing factors and occurrence processes of MS events.