Research on hard roof fracturing stress transfer technology for protecting uphill roadways: a case study of Qianyingzi Coal Mine

Hard roofs exhibit high integrity and substantial thickness, acting as effective media for mining-induced stress transmission. These characteristics frequently lead to instability and significant deformation of surrounding rock in district uphill roadways. This study focuses on the W3₂33 working face at the Qianyingzi Coal Mine. A combination of theoretical analysis, numerical simulation, and field testing clarifies the stress distribution within the surrounding rock after fracturing. The research proposes and applies a hydraulic fracturing roof-cutting technique to protect district uphill roadways. Results indicate that fracturing optimizes the stress environment. The maximum stress decreases from 33.4 MPa to 24.6 MPa, and the minimum stress reduces from 22.3 MPa to 7.7 MPa. Average stress reductions reach 25.8% on the left side and 39.6% on the right side of the uphill roadway. Consequently, stress concentration in the surrounding rock alleviates significantly. Retreating staged fracturing creates a dynamic pressure blocking line within the hard roof between the district uphill and the working face stop line. Such a blocking line disrupts stress propagation through dense sandstone layers to control roadway deformation. Borehole hydraulic connectivity and water pressure curves characterize fracture propagation to evaluate fracturing effectiveness. Fractures extend 15–20 m within 30 minutes after fracturing begins. Peak water pressures range from 31.2 MPa to 35.8 MPa in sandstone and 23.7 MPa to 26.4 MPa in mudstone. The mudstone peak pressure represents approximately 74.8% of the sandstone value. Post-fracturing convergence of the roof, floor, and ribs remains below 95 mm and 87 mm, respectively. These data confirm that roof hydraulic fracturing effectively blocks mining-induced stress transmission to the district uphill. This study provides a practical engineering case and serves as a reference for deformation control under similar geological conditions.