Strong dynamic mining pressure behavior in gob-side roadways and multi-level pressure relief prevention and control of thick-hard and overlying roof

In order to improve the mine pressure behavior of strong dynamic load caused by high stress in secondary reuse roadway, based on the mining geological conditions and mechanical parameters of directly covered hard thick roof coal seam, the methods of drilling observation, MEMS tilt sensor monitoring and theoretical analysis are adopted. The caving characteristics of lateral roof under unilateral goaf are studied, the surrounding rock deformation characteristics of goaf roadway are analyzed, and the mechanism of strong load pressure behavior of goaf roadway with direct hard thick roof is revealed. The results show that: the straight covered hard thick roof exists in the state of “suspended beam” in the lateral direction of the working face, and the length of the suspended beam is 28.8 m. Mining activities have revealed specific microseismic features in roof fracturing. In the vertical direction, the strong dynamic load mine pressure in gob-side roadway is dominated by low roof strata within the range of 30 m. In the inclination, microseismic events are mainly concentrated on the side of the goaf, with fewer events occurring in the central part of the working face and near the side of the adjacent working face,which shows that the roof collapse is insufficient. After the mining of the adjacent working face, the stress on the coal pillar side of the gob-side roadway is greater than that on the coal mining side, and the stress distribution of surrounding rock on the coal pillar side and coal mining side is asymmetrical. Under the influence of the insufficient lateral collapse of the hard thick roof directly covered in the goaf, the stress has been maintained at a high level, which leads to the strong dynamic load pressure in the gob-side roadway during the mining of the working face. For this reason, the multi-level pressure roof relief technology of blasting combined with fracturing is put forward to control the roof of secondary reuse roadway ahead of mining, which effectively separate the roof in the central and corner areas of mining face, as well as the roof in the corner areas of the adjacent mining face. Before the secondary reuse tunnel is impacted by dynamic pressure, proactively manage the tunnel roof. Regulating the stress distribution in the surrounding rock of the adjacent empty tunnel at its source ensures the timely collapse of the lateral roof in the mined-out area. After pressure relief, the overall deformation of the roadway is reduced to less than 10% of the roadway section, the influence range of abutment pressure and stress concentration of coal pillar are significantly reduced, and the surrounding rock stress environment of the gob-side roadway is improved.