Key technologies for mining-induced stress evolution and dynamic disaster prevention in extra-thick coal seams

Addressing the challenges in the deep mining of China’s extra-thick coal seams—where mining disturbances readily induce dynamic hazards, and gas control is hindered by issues such as blind spots in borehole coverage and the insufficient reliability of effectiveness verification—this study was conducted with the single extra-thick, outburst-prone coal seam at the Jinhe Coal Mine in the Yaojie Mining Area as its engineering context. It systematically investigated the dynamic evolution of the stress field throughout the entire mining process, the optimization of key technologies for regional outburst prevention at the working face, and techniques for high-efficiency pressure relief and permeability enhancement in local stress zones at the driving face.FLAC3D numerical simulations revealed the developmental characteristics of the arc-shaped pressure relief zone in a fully-mechanized top-coal caving face with a large mining-to-caving ratio: the zone's width was 5～7 m during the initial mining period, 3～5 m in tectonic zones, and 10～15 m in normal zones. Concurrently, it was discovered that under the superposition of multiple mining-induced stresses, an ultra-high stress concentration phenomenon occurs at the driving face, with the stress concentration factor (λ) reaching as high as 2.4～3.0. Accordingly, a graded risk management and control method based on dominant stress factors was proposed: the longwall face was zoned into a Grade I risk area (λ>2.0) and a Grade II risk area (1.5≤λ≤2.0), while a Grade III risk area (1.0≤λ<1.5) was established for the driving face, for which differentiated prevention and control countermeasures were developed. To address the challenges associated with traditional regional prevention techniques at the working faces, four key technologies were developed and applied to enhance the reliability of outburst prevention: A 3D inversion system for regional measure boreholes, which achieves 3D visualization of borehole trajectories and identification of risk areas, thereby eliminating “3D weak zones” in regional borehole coverage; A stratified and three-dimensional prediction model for gas drainage compliance, which uses the minimum drainage radius of the top slice as the standard for borehole layout to ensure the middle and upper parts of the coal body are fully drained; An inner-liner, wall-clinging gas content sampling device that reduces gas desorption loss, increasing the measured desorbable gas content by 6.25% to 20.59% compared to traditional borehole collar sampling; A “by-zone, by-band, by-layer” full-coverage verification method, which intensifies testing in high-risk areas like tectonic zones and soft coal bands and validates key horizons layer by layer, reducing verification blind spots. For high-stress zones at the driving face (such as the 16219⁻¹ driving face, affected by sevenfold mining influence), an improved ultra-high-pressure hydraulic slotting technology and its associated equipment (including high-rigidity lightweight drill rods, an anti-slip device, and a water quality filter) were applied. The results showed that in the high-stress zone of the 16219⁻¹ driving face, the stress concentration factor decreased from 3.0 to 1.6, the coal seam’s permeability coefficient increased 10-fold, the time required to meet drainage standards was shortened by one-third, and the residual gas content was reduced to 4.73 m³/t. During driving, CH₄ and CO₂ gushing remained stable (with a maximum CO₂ concentration of 0.48%), and high-energy microseismic events decreased, achieving the “dual” objectives of outburst elimination and stress reduction.