Formation process of thrust faults in coal measures and its influence on mining disaster

In order to better understand the formation of thrust fault in coal measures and how it makes a difference on mining-induced disasters, a simulation system for the formation process of a new type of thrust fault in coal measures has been improved, which adopts hydraulic servo control to realize the double precise control of displacement and stress. During the coal seam mining test, only part of the transparent plate at the mining position behind the coal seam is removed to keep the internal structural stress from being released. The system is used to carry out the experimental research on the formation of thrust fault in coal measures and coal winning operation. The results indicate that the displacement of each rock stratum can be divided into three regions during the formation of thrust fault: displacement region, compression region and stability region. The maximum displacement of the measuring point is in the displacement region and the relative displacement in various measuring points is small, its extents increase with the decrease of the burial depth of rock stratum. The displacement of measuring points in the compression region gradually decreases from hanging wall to footwall, and the displacement and relative displacement in the stability region are both the smallest, and their extents decrease with the burial depth of the rock stratum. The displacement angle of hanging wall measuring point increases gradually as the measuring point approaches the fault plane, reaching a maximum of 87.5°. In the formation of thrust fault, the horizontal stress on the roof and floor increases and then decreases, and the horizontal stress on the hanging wall is greater than that at the foot wall. The vertical stress of the coal roof in the foot wall of the fault tends to increase, while the vertical stress of the coal seam roof in the hanging wall of the fault tends to present the change of increase−decrease – increase. When comparing and analyzing the in-situ stress measurements of 22 domestic thrust faults in coal measures, it suggests that the ratio of maximum horizontal principal stress to vertical principal stress is in the range of 1−4 in the tectonic zones of thrust fault. After the thrust fault is stabilized in the test, the k of the hanging wall and foot wall is stable between 2−3. After the formation of thrust fault in coal measures, in the footwall coal seam mining process, the vertical and horizontal stresses in the coal seam roof both tend to increase and then decrease. Under the superposition of tectonic stress and mining-induced stress, the rock stratum near the fault produces stress aggregation, and its peak stress is greater. The conditions mentioned above lead to more violent movement of the overlying strata after coal winning. The coal winning can be divided into the cyclic evolution stage of rock pressure and the dynamic disaster stage. In the cyclic evolution stage of rock pressure, the vertical stress of wall and working face increases significantly periodically, and the high stress area migrates to the footwall structure coal. In the dynamic disaster stage, the working face is already in high stress area, which is easy to cause coal mine dynamic disasters such as rock burst.