Precise three-dimensional borehole pressure relief technology for surrounding rock control of large deformation roadways in high-stress coal seams.

Abstract

To address the large deformation control problem of surrounding rock in high-stress roadways subjected to multiple disturbances, the 112 transport crosscut of Laoyingshan Coal Mine in Guizhou Province was taken as the engineering background. The deformation and failure mechanism of surrounding rock in disturbed high-stress roadways was investigated by theoretical analysis, numerical simulation, drilling cuttings testing and field monitoring. A three-dimensional precise borehole pressure-relief control technology based on the identification of the stress peak zone was proposed, and the effects of key pressure-relief parameters and engineering application were analyzed. The results show that the superposition of repeated mining in multiple coal seams, adjacent roadway excavation and concentrated coal-pillar stress causes continuous redistribution of surrounding-rock stress. The migration of peak stress toward deeper zones and the expansion of the plastic zone are the dominant factors inducing non-stationary plastic large deformation of the roadway. The proposed precise three-dimensional borehole pressure-relief technology reconstructs the stress-transfer path of the surrounding rock, transfers high stress from the shallow anchorage-controlled zone to the deeper stable zone, and preserves a load-bearing elastic structure in the shallow zone, thereby forming a coordinated control mode of "shallow load bearing and deep pressure relief". Parameter analysis indicates that borehole diameter, depth and spacing are strongly coupled. An excessively small diameter is insufficient to form an effective pressure-relief zone, whereas an excessively large diameter may damage the anchorage zone. The borehole depth should match the stress peak zone, and the spacing should ensure the continuity of the pressure-relief zone. In the field application, the stress peak zone of the 112 transport crosscut was identified by the drilling cuttings method, and a pressure-relief scheme with a borehole diameter of 133 mm, spacing of 2 m, depth of 38 m on the east side and 32 m on the west side was adopted. Field monitoring and numerical results show that the plastic zone was significantly reduced after pressure relief, and in the left rib section adjacent to the New First Mining Area haulage rise, specifically the 0-33 m section, the deformation reduction reached 82.23% after pressure relief. Borehole imaging results were consistent with the identified stress peak zone. The research results provide a reference for surrounding-rock stability control in disturbed high-stress roadways.