Mechanism and key parameters of stress load-off by innovative asymmetric hole-constructing on the two sides of deep roadway

Traditional dense large-diameter borehole stress load-off techniques reduce the stress levels in the shallow surrounding rock, weaken the bearing capacity of the shallow surrounding rock, and greatly deteriorate the shallow surrounding rock strength and supporting structure, which is not conducive to maintaining the long-term stability of the roadway. Therefore, to address the control problem for the pronounced extrusion deformation in the two sides of a roadway and the overall outward movement of the shallow surrounding rock supported by the sides bolts and anchor cables, as well as to comprehensively consider the on-site construction conditions of the two sides of a test roadway, stress load-off technology for asymmetric hole construction on the two sides of a roadway is proposed. The asymmetric stress load-off technique is a new method; while the shallow surrounding rock of the roadway sides is strongly anchored via a full anchor cable support form, a group of large stress load-off holes near the deep stress peak line of the roadway sides is excavated to relieve pressure and protect the roadway. This technology can transfer the peak stress area of the roadway side deeper into f the surrounding rock without deteriorating the shallow surrounding rock strength and damaging the supporting structure. A numerical simulation analysis of asymmetric stress load-off on the two sides of the roadway was performed, the stress load-off effect evaluation index was established, and the optimal field construction parameters were obtained. The stress load-off parameters obtained from the study are applicable to field engineering practice. Mine pressure data reveal that the test roadway remains intact and stable during the use period when the asymmetric stress load-off technique is adopted.