Waterjet Cutting Sandstone Ability Test and Process Parameter Optimization Research

In China, 90% of the outburst accidents are directly related to the hard roof overburden. To enhance the top-pressure relief effect of the pre-determined directional fractures by water jet cutting, this study selected relatively hard fine-grained sandstone in the underground coal mine as the test material. Through single-factor experiments and orthogonal experiments, the influence laws of water jet process parameters (jet pressure, horizontal movement speed, cutting target distance, abrasive concentration, and cutting angle) on the rock-cutting ability were systematically analyzed. The SPH-FEM coupling method was adopted to simulate the rock-breaking process of water jet-cutting fractures. The results of single-factor experiments showed that jet pressure was positively correlated with the rock-cutting characteristic index, while lateral displacement speed was negatively correlated with it. The cutting depth showed a trend of increasing first and then decreasing with the increase of cutting target distance and abrasive concentration. The optimal target distance was 10 mm, and the optimal abrasive concentration was 12%. The cutting angle showed two depth peaks at 80° and 100°, indicating that adjusting the angle could significantly improve the cutting efficiency. The results of the four-factor five-level orthogonal experiments showed that in the case of a fixed abrasive concentration, the primary and secondary factors affecting the cutting depth were jet pressure, horizontal movement speed, cutting angle, and cutting target distance. The optimal parameter combination for water jet cutting fine-grained sandstone was jet pressure 60 MPa, horizontal movement speed 100 mm·min-1, cutting target distance 20 mm, and cutting angle 85°. Based on the experimental results, a cutting-depth prediction model for fine-grained sandstone was constructed. The numerical simulation indicated that the abrasive water jet impact induced shear failure of the rock unit under the compression stress dominance, and the stress field showed a dynamic evolution characteristic of gradient attenuation from the impact center to the edge, forming an incremental damage area centered on compression failure. The prediction model and simulation results provided a theoretical basis for the optimization of water jet cutting technology, and the research results have important practical reference value for the top roof top-pressure relief engineering in coal mines.