Synergistic Roof Key-Strata Hydraulic Fracturing and In-Seam Static Expansion to Create a Dual Pressure-Relief Field for Deep Coal Seam Gas Exploitation

Deep coal mining encounters substantial challenges associated with diminished permeability and elevated gas pressure under multi-physics coupling conditions. This paper introduces an innovative methodology that integrates the staged high-pressure hydraulic fracturing of roof key strata with the static expansion fracturing of coal seams using solid expansive materials. The proposed technique facilitates the coordinated regulation of the stress and fracture fields, enabling efficient stress relief, long-term anti-reflection performance, and low-damage seam modification. By employing theoretical modeling based on Hamilton’s canonical equations, conducting experimental impact tests, and performing field validation, this research demonstrates that the synergistic strategy markedly alleviates stress concentration by more than 25%, increases permeability by a factor of 3.7, and enhances gas extraction efficiency while preserving fracture network stability. The results indicate sustainable gas drainage characterized by reduced decay coefficients, offering a reliable and efficient approach for strata pressure management and gas disaster mitigation in deep mining operations. This integrated solution contributes to both safety enhancement and resource recovery optimization under complex geo-mechanical conditions.