Influence of fracturing spacing on rock mass fracturing and energy evolution in overlying strata

In the mining of extra-thick coal seam with hard roof, the large roof fracture step and high strength are prone to cause dynamic disasters in the stope. Ground fracturing technology can form an artificial large-scale fracture network in the hard roof to weaken the rock mass fracture strength, which is an innovative and effective technical to control the dynamic disasters. Combining laboratory test and numerical simulation, this paper systematically studied the regulation mechanism of different ground fracturing spacings on the rock fracture mechanical behavior and energy evolution of overburden. Uniaxial compression tests on sandstone specimens with prefabricated cracks, combined with DIC-based crack propagation monitoring, revealed how fracture spacing governs rock mass strength, brittleness indices, and failure mechanisms. The research shows that prefabricated cracks significantly reduce rock mass compressive strength and brittleness indices, with peak strength reduction occurring at 20 mm double-fracture spacing and 5 mm triple-fracture spacing. Based on the coupled model of FLAC 3D and PFC 3D , the internal correlation between fracturing spacing and overburden energy evolution was revealed. Ground fracturing changes the energy release form to energy-damp and energy-slip dissipation by reducing the fracture step of the hard roof. When ground fracturing spacings at 30 m and 10 m, the increment of energy-body in the hard roof was reduced by more than 26 %, the energy accumulation in the hard roof was significantly weakened, and the dynamic disasters in the working face can be significantly prevented and controlled.