Research on the pre-splitting technology of composite hard roof with deep-shallow hole coordinated blasting based on the thin plate theory

The composite hard roof in the southeastern Shanxi mining area exhibits characteristics of low-level large-span suspended roof and high-level extensive delamination, which can easily induce creep deformation or impact dynamic disasters in the roadways. To improve the stope boundary morphology and promote roof rotation and subsidence, a technique for maintaining roadway integrity and mitigating impact disasters by using deep-shallow hole cooperative blasting to induce mutual feedback and collapse of high-low level roofs is proposed. Research indicates that the transformation of the goaf boundary from a fixed end to a simply supported end liberates the boundary constraints of the roof. Leveraging the deep-shallow hole cooperative guidance mechanism, the role of the shaped charge tube in controlling the shaped charge flow, and the mutual feedback mechanism between high-low level roofs, the development length of blasting fractures in the axial direction of the roadway is significantly extended, creating basic conditions for the transformation of the fixed end into a simply supported end. The construction parameters for pre-splitting blasting of the roof in the cutting and extraction roadways have been determined through theoretical calculations and field engineering cases. Engineering practice shows that the blasting holes in the cut-off tunnel prompt the initial roof of the working face to change from a four-end fixed support to a three-fixed and one-simplified support. The initial pressure step distance of the working face is reduced by 28% after the pre-splitting blasting of the cut-off tunnel roof. The deep and shallow hole coordinated blasting in the 13132 roadway forms a dense fracture zone 18 to 40 meters above the coal seam, improving the boundary conditions of the roof of the transport entry and weakening the energy storage property of the roof. The energy of 88% of the microseismic events in the 13132 roadway area is reduced to 12500 to 27500 joules. The periodic pressure step distance and dynamic load coefficient of the 1312 working face are reduced to 9.5 meters and 1.27 respectively. Both the pressure step distance and pressure intensity are decreased. This indicates that deep-shallow hole cooperative blasting pre-splitting can effectively improve the morphology of the composite hard roof at the stope boundary and play a role in maintaining roadway integrity and mitigating impact disasters during extraction work.