Abstract: To address the technical challenges of random crack direction, low energy utilization efficiency, and frequent blowouts in conventional perfusion static fracturing of coal and rock masses, a static fracturing method based on a directional energy-concentrating structure is proposed. Comparative experiments were conducted using three charging forms—conventional perfusion, directional structure, and directional energy-concentrating structure—on a self-built static fracturing test platform for coal and rock. The experiments utilized artificial rock-like materials to prepare cubic specimens with different borehole diameters, simulating the hard roof sandstone in the northern region of Shanxi province. The dynamic propagation of cracks was monitored in real time using digital image correlation technology. Three quantitative indicators—average crack initiation time, average fracture aperture, and crack propagation rate—were introduced to comprehensively evaluate the static fracturing effects under different charging structures. The results demonstrate that the directional energy-concentrating structure effectively guides the concentrated release of expansion stress from the static cracking agent along a predetermined direction, significantly suppressing energy dissipation and enabling directional crack initiation and propagation. Macroscopically, specimens tested with the directional energy-concentrating structure exhibited flatter and more integrated fracture surfaces, showing a clear three-stage evolution characteristic: “directional force application–linear cracking–planar coalescence.” Mesoscopic strain field analysis revealed that the displacement gradient and strain concentration were significantly higher than those in conventional perfusion and directional structure tests, with a maximum apparent displacement vector of 2.98 mm. For instance, in specimens with a 50 mm borehole diameter, the crack initiation time was 23.8 min, the average fracture aperture was 2.89 mm, and the crack propagation rate reached 1.46 m/s. These values represent improvements of 36.2%, 56.8%, and 99.3%, respectively, compared to conventional perfusion tests, and 14.7%, 51.7%, and 92.8% compared to directional structure tests. The findings validate the mechanical superiority and technical feasibility of the directional energy-concentrating structure in static fracturing, providing a theoretical and experimental basis for applying static fracturing technology to weaken and relieve pressure in deep high-stress hard rock masses.

Key words: static fracturing, directional energy concentration, expansion stress, crack propagation, digital image correlation technology