A discrete element study of the fracture propagation of rock-like materials under directional sleeve fracturing

Abstract

The frequent occurrence of rockburst accidents caused by the fracture of hard roof strata with the increase in mining depth has made it necessary to investigate methods for preventing and controlling such dynamic disasters. To reveal the characteristics of rock fracture under sleeve fracturing, the experiments for expansion pressure measurement of the sleeve and the experiments for single-hole sleeve fracturing were performed. The influence of the expansion path of the sleeve wall on the expansion pressure is analyzed based on the discrete element method. A numerical sleeve fracturing model is calibrated, based on which the mechanism of multiple-hole sleeve fracturing of rock is elucidated. The results show the following. The expansion pressure is linearly related to the injection pressure, and there is pressure loss during the injection process, with a maximum loss of 9.73 MPa, accounting for approximately 28 % of the maximum injection pressure. Within the safe pressure range, the expansion pressure increases exponentially. The sleeve fracturing process can be approximately simulated by adjusting the microscopic parameters of the model and the expansion path. Combining prefabricated slots and sleeve fracturing can effectively achieve directional fracturing of the rock. The model with prefabricated slots has a lower fracturing pressure under different confining pressures. Under the conditions of no confining pressure, σx = 1 MPa and σy = 2 MPa, and σx = 2 MPa and σy = 1 MPa, the peak stress of the model with slots is 12.24 %, 7.32 %, and 9.84 % lower than that of the model without slots, respectively. The calculation formulas for circumferential stress at a point on the line connecting borehole centers, fracture propagation angle, and stress distribution near the slotted tip are derived theoretically, revealing the mechanical mechanism of directional sleeve fracturing of the rock.