Xuesheng Liu

In Situ Investigations on Failure Evolution of Overlying Strata Induced by Mining Multiple Coal Seams

Accurate evaluation of the failure evolution of the overlying strata after multiple mining actions is of great importance both for the prevention of water disasters and the mining designs. To ensure the safety of mining multiple coal seams, the fracture criterions of overlying strata after mining actions were established on the basis of beam theory as well as the influences of coal seam spacing, face size, and lithology on the increased heights of failure zones after each consecutive mining sequence. A newly developed device, named electric controlled water flow detector, and its detecting procedure, was introduced. In situ investigations were performed in the Gaojialiang and Jinhuagong Mines, China. Results showed that the mining of a lower coal seam does not change the failure evolution of the roof strata of the upper coal seam when the coal seam spacing is large. The larger the mining height of the lower coal seam is, the more fractures the overlying strata of the upper coal seam have, and the larger the height of the failure zone. In addition, the failure extent of overlying strata caused by coal face mining increased with their hardness. It was found that the electric controlled water flow detector can effectively detect the failure evolution during multiple mining actions, with high water plugging effectiveness and detection accuracy.

Pattern Recognition of Signals for the Fault-Slip Type of Rock Burst in Coal Mines

The fault-slip type of rock burst is a major threat to the safety of coal mining, and effectively recognizing its signals patterns is the foundation for the early warning and prevention. At first, a mechanical model of the fault-slip was established and the mechanism of the rock burst induced by the fault-slip was revealed. Then, the patterns of the electromagnetic radiation, acoustic emission (AE), and microseismic signals in the fault-slip type of rock burst were proposed, in that before the rock burst occurs, the electromagnetic radiation intensity near the sliding surface increases rapidly, the AE energy rises exponentially, and the energy released by microseismic events experiences at least one peak and is close to the next peak. At last, in situ investigations were performed at number 1412 coal face in the Huafeng Mine, China. Results showed that the signals patterns proposed are in good agreement with the process of the fault-slip type of rock burst. The pattern recognition can provide a basis for the early warning and the implementation of relief measures of the fault-slip type of rock burst.

Multiparameter Monitoring and Prevention of Fault-Slip Rock Burst

Fault-slip rock burst is one type of the tectonic rock burst during mining. A detailed understanding of the precursory information of fault-slip rock burst and implementation of monitoring and early warning systems, as well as pressure relief measures, are essential to safety production in deep mines. This paper first establishes a mechanical model of stick-slip instability in fault-slip rock bursts and then reveals the failure characteristics of the instability. Then, change rule of mining-induced stress and microseismic signals before the occurrence of fault-slip rock burst are proposed, and multiparameter integrated early warning methods including mining-induced stress and energy are established. Finally, pressure relief methods targeting large-diameter boreholes and coal seam infusion are presented in accordance with the occurrence mechanism of fault-slip rock burst. The research results have been successfully applied in working faces 2310 of the Suncun Coal Mine, and the safety of the mine has been enhanced. These research results improve the theory of fault-slip rock burst mechanisms and provide the basis for prediction and forecasting, as well as pressure relief, of fault-slip rock bursts.