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The huge impact of kinetic energy released by the breaking of hard roof is one of the important factors that induces dynamic disasters in coal mines. The key to preventing and controlling coal and rock dynamic disasters is the directional fracture of strata at a specific position and reducing the length of hard roof suspension. The multi-hole sleeve fracturing technology has the advantages of simple operation and wide application conditions and has a wide research prospect in the field of hard roof weakening. In order to understand the mechanism of multi-hole sleeve fracturing, the mechanical mechanism of multi-hole sleeve fracturing was studied using theoretical analysis and numerical simulation. The variation law of inter-hole stress under different influencing factors was revealed, and the crack propagation law and force chain distribution characteristics in the fracturing process were obtained. The pre-cracking effect of sleeve fracturing can be improved by changing the drilling structure through grooving. In order to determine the reasonable hole arrangement parameters, a mechanical model of the multi-hole sleeve fracturing with prefabricated cracks was established based on linear elastic fracture mechanics. The calculation equations of stress intensity factor, critical expansion pressure, and critical crack initiation angle of cracks were given, and the variation rules of stress intensity factor, critical expansion pressure, and critical crack initiation angle of cracks under different influencing factors were obtained. The results show that: ① The lateral pressure coefficient k has a significant effect on the minimum crack initiation stress of the borehole. With the lateral pressure coefficient k > 1, the minimum crack initiation stress decreases with the increase of the hole angle. With the lateral pressure coefficient k < 1, the minimum crack initiation stress decreases with the increase of the hole angle. ② The numerical simulation results show that there is a stress superposition effect between the sleeves, and the contact force chain is a 'radial' distribution. The fracturing process of the sleeve is mainly a tensile failure, and the deformation and failure at the connection of the hole center is the most severe, forming a 'banded' fracture surface along the direction of the hole. ③ The stress distribution near the slot end is changed by the slot, and the circumferential tensile stress is larger than that of the seamless slot model. When the slot length is 0.5 times the radius of the hole, the critical expansion pressure is the smallest, and the crack is most likely to expand. ④ The critical initiation angle is determined by KI and KII, which is less than 70.53°. Under the condition that the pump pressure and in-situ stress conditions cannot be changed, the directional fracturing of the rock can be realized by adjusting the hole angle and the length of the prefabricated slot.

In order to reveal the micromechanics of rock failure mechanisms and energy transfer patterns under different confining pressures during sleeve fracturing, a PFC3D numerical model was established based on sleeve fracturing tests and expansive force measurement experiments. The discrete element method was employed for the numerical simulation of the sleeve fracturing process. In addition, by integrating acoustic emission data, the influence of varying confining pressures on the development of microcracks in rocks and the corresponding energy variations were explored. Furthermore, the mechanical mechanism for sleeve fracturing was revealed based on the principles of elasticity. The results show that : ① There is a pressure loss in the process of sleeve liquid injection. According to the pressure loss rate, the liquid injection process can be divided into three stages: filling, pressurization, and rapid pressurization. The expansion force of the sleeve exhibits a linear relationship with the injection pressure, with a correction coefficient of 0.678. ② The PFC3D numerical model effectively represents the mechanical properties and deformation failure characteristics of rocks during sleeve fracturing, where tensile failure is the predominant mode of rock fracturing. The propagation path of cracks is determined by the confining pressure, which also suppresses the generation of microcracks within the rock. As the differential stress increases, both the number and proportion of shear cracks inside the rock gradually increase. ③ Acoustic emission signals can be divided into quiescent and active periods, with the cumulative number of cracks showing a stepwise increase. The characteristics of acoustic emission exhibit a single-peak distribution under unconfined conditions and a multi-peak distribution under confined conditions, indicating the presence of multiple fracture stages. ④ The influence scope of the sleeve expansion force is limited, and the sleeve expansion force exhibits a logarithmic correlation with the circumferential tensile stress. The tangential stress increases with the increase of stress difference. When the angle φ is 45° or 135°, the shear damage inside the rock is most obvious. ⑤ The energy input into the rock decreases as the confining pressure increases under the same expansive force. Under different confining pressures, the input energy, elastic energy, and dissipation energy of rock increase sharply in different degrees, which is mainly due to the expansion of the borehole caused by the formation of macro cracks. The growth rate of dissipative energy is faster than the elastic energy, approximately 1.27 to 1.55 times that of the elastic energy.