Effect of detonating position of deep-hole cumulative blasting on coal seam cracking and permeability enhancement

This paper is concerned with the effect of detonating position of deep-hole cumulative blasting on coal seam cracking and permeability enhancement.Based on the analysis of the propagation of detonation wave and the distribution of explosion stress field, the formation of cumulative energy flow and the development of coal crack under the conditions of different detonating positions were studied by numerical simulation.Then, according to the gas geological conditions of the coal seam in the No.10 mine of Pingdingshan, the field tests of deep-hole cumulative blasting in coal seam were carried out.The results indicate that the initiation position have an influence on the development of coal rock blasting cracks, by controlling the propagation mode of detonation wave and stress wave in cumulative charge.Detonation wave collision and stress wave superposition effect are important reasons for the uneven distribution of explosive cracks along the axis of charge.The effect of deep-hole cumulative blasting initiated at different positions makes the fracture development show different characteristics.When the charge is detonated at one end, the stress field around the blasting hole increases gradually along the propagation direction of detonation wave, and the range of detonation cracks increases gradually from the initiation end to the other end of the charge.Besides, under the condition of simultaneous detonation at both ends, the detonation overpressure formed by detonation wave collision drives the energy accumulation grooves to collide with each other to produce cumulative flow with greater kinetic energy, which acts together with the superposition of explosion stress waves to expand the range of local cracks.Furthermore, under the condition of three-point simultaneous detonation, the detonation wave collision and conical stress wave are superimposed near the trisection point of the charge, resulting in the formation of a wider range of cracks.With the increase of the initiation point, the charge length between the initiation points is shortened accordingly, which weakens the superposition effect between conical stress waves, reduces the gap between the development range of explosive cracks at the impact point of detonation wave and that at other positions, and makes the explosive cracks distributed more evenly along the axis of charge.