Study on fracture instability and energy accumulation-release evolution of thick-hard roof in stope

In order to address the strong mining pressure of thick-hard roof, in this paper, the mining-induced bearing mechanical model was established based on the instability influence analysis of thick-hard roof. The evolution law of the mining bearing state and energy accumulation of thick-hard roof was investigated. From such energy transfer perspective, the mechanical relationship between the accumulated energy release caused by the thick-hard roof breakage and the associated strong dynamic pressure appearance was analyzed. On this basis, the dynamic load response estimation equation of hydraulic support in the working face was derived to reveal the characteristics of impact from the strong mining pressure caused by the thick-hard roof breakage. The conclusions drawn from this paper are as follows. Firstly, the thick-hard roof is in the state of bearing the overburden, with its own elastic potential energy accumulating before the fracture instability. In case of fracture instability, the thick-hard roof shows a slightly higher level of accelerated motion instability compared to gravity, and the overhang span of the broken block is large, which leads to the high dynamic pressure on the working face due to the instability of thick-hard roof. Secondly, overhanging span and overburden load are the significant influencing factors for the evolution of mining bearing capacity, as well as the energy accumulation and release in the thick-hard roof, where the overburden load, thickness and strength are the crucial influencing factors in the ultimate overhanging span of thick-hard roof. Thirdly, as for the composition of the strong dynamic pressure behavior in the working face for thick-hard roof, the dynamic resistance caused by the cumulative energy release accounts for the largest proportion, followed by the dynamic resistance caused by the work of the overlying rock load. Lastly, among the influencing factors of dynamic resistance response of hydraulic support in working face, the overhanging span and the load of the overlying strata play a direct role in causing aggravation, and the rock thickness plays an indirect role in causing aggravation by increasing the limit on overhanging span of the thick-hard roof, where the direct roof thickness can buffer and reduce the dynamic resistance response, and the roof control distance of the support plays a role in causing aggravation, but not to a significant extent. © 2022, Editorial Board of Journal of Mining & Safety Engineering. All right reserved.