Study on static expansive fracturing for pressure relief and rockburst prevention in coal seam boreholes

Addressing the insufficient pressure relief in the deep coal mass and the deterioration of the surrounding rock bearing structure due to increased borehole diameter in conventional borehole pressure relief techniques, a static expansive fracturing method for pressure relief in coal seam boreholes is proposed. A critical stress model for static expansive fracturing in coal seam boreholes is established through theoretical analysis, and numerical simulations are conducted to compare and analyze the differences between this method and conventional borehole pressure relief techniques in terms of roadway pressure relief effect and surrounding rock stability control. The results indicate that using a 150 mm borehole with a 75 MPa expansive stress achieves a comparable state of full pressure relief in the rib coal as a 250 mm borehole, while increasing the pressure relief range in the deep coal mass by a factor of approximately 3.6. Although conventional borehole pressure relief methods can enhance pressure relief by increasing the borehole diameter, they significantly expand the plastic zone in the shallow surrounding rock, aggravating surrounding rock deformation. In contrast, the static expansive fracturing method for pressure relief in coal seam boreholes actively directs fractures in the deep high-stress coal mass, promoting the expansion and interconnection of its plastic zone to form a deep structural weakening zone, while markedly reducing the disturbance and damage to the shallow surrounding rock. This method breaks through the limitations of passive borehole for pressure relief, offering dual advantages of efficient deep pressure relief and shallow surrounding rock stability protection, and providing a new approach for rockburst prevention.