Study on the application of shallow hole blasting to roof cutting and pressure relief in gob side entry with thick and hard roof

Aiming at the problems of large-area overhanging roof and large deformation of the filling body, the use of shallow-hole blasting to cut the roof to relieve pressure is one of the effective way to optimize the surrounding rock structure of the gob-side entry retaining with thick and hard roof. Taking the thick and hard roof of Sanhejian Coal Mine as the engineering background, using LS-DYNA numerical simulation and theoretical calculation method, the mechanism of roof cutting and pressure relief by shallow hole blasting is analyzed, and the reasonable parameters of roof cutting and pressure relief along gob-side entry retaining are determined. The research results show that the blasting of adjacent blast holes can play a stress-oriented and superimposed effect, and the cracks are mainly caused by tensile fractures. The crushing area and the crack area provide a weak surface for the fracture of the thick and hard roof, and the thick and hard roof collapses in time, eliminating the danger of sudden pressure and impact damage caused by the sudden collapse of the large-area roof. Adopting the surrounding rock control technology of gob side entry retaining by shallow hole blasting combined with roof cutting and pressure relief and roadway side filling, the mechanical model of gob side entry retaining by shallow hole blasting is established, and the roof cutting parameters of 5 000 mm hole depth, 42 mm hole diameter, 1.3 charge decoupling coefficient, 900 mm hole spacing, 80° hole to gob side angle and 7.73 MN/m filling support resistance are determined. The research results have been successfully applied to the roof cutting and pressure relief engineering practice of the gob side entry in 72207 working face of Sanhejian Coal Mine. The surrounding rock of the side entry remains intact and the maintenance effect is good.