Numerical and experimental investigation on rock breaking mechanism and performance of high-pressure energy-gathering water jet

Addressing the issues of short target distance and small nozzle diameter in conventional jet rock breaking, which result in low rock breaking energy and difficulty in achieving efficient rock fragmentation, a high-pressure energy-gathering water jet (HEWJ) device is proposed. Firstly, the relationships between the radial, tangential and shear dynamic stresses of the rock and parameters such as “water hammer pressure” and the distance from the impact point of HEWJ were analyzed. By employing SPH-FEM algorithm, a “ball shaped” HEWJ rock breaking consistent with the theoretical model is established, revealing the stress variation patterns and crack propagation within the rock under the impact of HEWJ with different jet velocity, jet diameter, and surrounding rock stress. Finally, experimental studies were conducted to explore the time-effective characteristics, impact target distances and frequencies on the rock breaking performance. The results indicate that the HEWJ exhibits periodic changes. A single cycle mainly includes the energy storage stage and the impact stage, and the impact stage is very short, only 0.23 s. As the impact time lengthens, the rock breaking volume, the diameter and the depth of the crushing pit increase exponentially and finally tend to be stable. Regarding the impact target distance, the rock breaking volume and the diameter of the crushing pit initially increase but then decline, whereas the depth demonstrates a steadily decreasing tendency. When the flow rate of the hydraulic pump increases from 80 L/min to 140 L/min, the jet impact frequency increases from 0.1914 Hz to 0.3189 Hz and shows a linear growth. Moreover, the rock breaking volume, the diameter and the depth of the crushing pit all show an increasing trend with the growth of the impact frequency. The optimal impact frequency of the HEWJ on the rock is 0.3189 Hz, which indicates that the flow rate of the hydraulic pump is 140 L/min at this time.