Numerical simulation of multi-hole and same delay time of cumulative blasting in coal seam and its application

A model of multi-hole cumulative blasting was established by using ANSYS/LS-DYNA to study the mechanism of crack propagation and permeability increasing under the multi-hole cumulative blasting in coal seam.The model represented all of the explosion process, including the formation of shaped jet, the propagation and superposition of explosive stress waves.The variation of coal element stress with time under different holes spacing was analyzed.It was found that cumulative jet penetrated into coal seam after the explosive exploded.The explosion stress waves propagated along their respective directions and the explosion stress waves superposed finally.It was also found that the longer the distance between adjacent holes, the longer it took for the stress wave to superimpose.Comparison of unit stress of coal under different holes spacing, it was found that cracks first appeared around the hole, the cracks then spread mainly along the holes line.As long as the distance between adjacent blast holes is proper, the coal between the holes is equivalent to twice blasting effect.The cracks of coal were fully developed and interconnected with each other, and then it would increase gas extraction rate.Besides, the multi-hole cumulative blasting tests were carried out and the test results show that multi-hole cumulative blasting can significantly improve the permeability of coal.At the same time, the reasonable distance of adjacent cumulative blasting hole is determined.