Application of Cutting Roof Pressure Relief Pre-fracturing Technology in Fully Mechanized Caving Face in Extra Thick Coal Seam

In order to improve the top coal resources at both ends of fully mechanized top coal caving face in extra-thick seam and the recovery rate of coal resources during the initial caving, reduce the impact of initial weighting on the working face during the initial caving, and reduce the rock pressure behavior during the mining period near the working face, the fracture damage theory is used to analyze the change of the breaking and caving step distance of roof rock girder and the initial pressure strength of fully mechanized top coal caving face after the roof cutting and unloading. It is concluded that the support pressure area of fully mechanized caving face moves forward, which enhances the caving ability of coal seam and the recovery rate of coal resources during the initial caving period. Taking a fully mechanized caving face of a coal mine in Shanxi Province as the research background, this paper compares and analyzes the difference between the first weighting step and the first caving step of fully mechanized caving face with or without roof-cutting pre-fracturing before initial mining and at the end of two roadways. The results show that the first weighting step of fully mechanized caving face is shorter 11.1 m than that of non-pre-fracturing after the implementation of roof-cutting pre-fracturing technology, and the first caving step is 16 m earlier than that before the pre-splitting; and by using borehole peeping technology, it is concluded that the top coal suspended in the triangle area of goaf breaks down along the fissures induced by pre-cracking blasting, effectively solving the problem of overhanging roof in the goaf of two roadways.