Due to the opaqueness of rock and the limitation of detection technology, it is impossible to accurately describe the crack growth process and determine the law of rock breakage. Based on smoothed particle hydrodynamics and the finite element method (SPH-FEM), a numerical model for high-speed water jet breaking was established in this work to simulate the fragmentation process of rock impacted by a high-speed water jet, and to study the effects of different jet angles on the propagation of microscopic cracks inside the rock. Additionally, we further analyzed the jet impact angle on the microscopic crack propagation trend of the rock by applying confining pressure to the rock. Theoretical and experimental analyses showed that the inclination angle of the jet determined the direction of axial crack propagation in the tension-type center. When the inclination angle of the jet exceeded 20°, the ability of water jet erosion was insufficient, and the efficiency of rock fragmentation was low. However, in the range of 15° to 20°, the capacity of erosion was strong, lamellar crack propagation was obvious, and rock chip block spalling was easily produced. The impact of the water jet on the rock at varying angles under rock confining pressure will make the crack propagation direction deviate from the direction without confining pressure and gradually become parallel to the rock plane, thereby promoting unilateral crack propagation in the direction of water jet impact, making the rock more likely to produce unilateral rock chip spalling.

Because of the unclear understanding of the characteristics associated with coupled rock breaking using multiple water jets, a numerical model combining smoothed particle hydrodynamics (SPH) and the finite element method (FEM) was established to investigate the rock-breaking capacity of a high-pressure, double-stranded water jet structure. The effectiveness of this model was verified through field experiments. The study further examined the specific energy required for rock breaking using the high-pressure double water jets and analyzed the effects of jet pressure, nozzle diameter, jet impact angle, and impact point spacing on rock-breaking volume. The results demonstrate that the rock-breaking ability of a high-pressure double water jets is better than that of a single water jet. When the impact angle of the high-pressure double water jets was 15° and the distance between impact points was 2.0 d, the rock damage effect was the best. By comparing the specific energies for rock breaking of a single water jet and a double water jet, it was concluded that the best rock-breaking nozzle diameter is 1.6 mm. Furthermore, an orthogonal testing approach was employed to determine the main and secondary factors influencing the rock-breaking energy of the high-pressure double water jet. The order of significance was found to be jet pressure > impact angle > impact point spacing > nozzle diameter. These findings provide valuable guidance and reference for application in the coal mining industry.