Research on Static Fracturing and Roof Caving Technology for Hard Immediate Roof in Fully Mechanized Mining Face Crossheading

Regarding the issue of initial mining roof hanging in fully mechanized mining faces, traditional technologies such as hydraulic fracturing and explosive blasting suffer from unstable effectiveness, high safety risks, and complex construction. Therefore, a green and efficient roof−caving technology based on a static cracking agent (C−SCA) is proposed. Experimental studies show that C−SCA exhibits high expansion characteristics similar to slurry−type cracking agents, with an expansion rate of 170−200% and an expansion pressure of 57.9 MPa. From an engineering perspective, the concept of the free expansion ratio of C−SCA was established, revealing that a larger free expansion ratio results in a lower final expansion pressure acting on the borehole wall. By applying confining pressure to concrete to simulate large−scale rock mass cracking conditions, it was found that a borehole spacing of 300 mm provides suitable stress conditions and crack propagation time for engineering applications. Using the CDEM numerical simulation method, the effect of roof−cutting and weakening measures on controlling hard roof strata was simulated and evaluated, comparing the roof collapse patterns under weakened and non−weakened conditions. In the weakened 15221 working face, the main roof fractured and collapsed within 10 m of mining, whereas in the non−weakened 15220 working face, collapse occurred only after 50 m. Analysis of monitoring data from the face−end supports shows that after static cracking, the working resistance of the face−end supports stabilized within the range of 25–35 MPa, with good synchronization between supports and low overall fluctuation amplitude. Moreover, comparisons of maximum support resistance, support working conditions, and duration of excessive resistance per support between the 15221 and 15220 working faces indicate that the face using C−SCA static cracking outperformed the face without static cracking. To further verify the effectiveness of C−SCA static cracking, on−site monitoring data from the two working faces were compared and analyzed. The air leakage volume during initial mining in the 15221 working face using static cracking technology was significantly lower than that in the 15220 working face. Dust concentration during production in the 15221 working face was also notably reduced compared to the non−cracked 15220 working face. The research results demonstrate that C−SCA has a significant effect on managing initial mining roof hanging, and the C−SCA static cracking technology provides a novel solution for treating hard roof hanging in initial mining faces.