Research And Application Of Fracture Distribution Law Of Coal Seam Permeability Improvement Technology By Blasting Through Floor Cross-measure Boreholes

In this paper,based on the law of gas flowing,the gas drainage technology and the theory of deep hole pre-splitting blasting,aiming at the problems that the drilling of the soft and low permeability coal in the coal body is easy to collapse,and low rate of the hole formation.It is difficult to achieve the problem of long-acting reinforcement.The method of increasing the concentration of the blasting group at the junction of the blasting coal seam and the rock is put forward in this paper.Through theoretical analysis,similar simulation test,numerical simulation and field test method of the route were carried out under different control pore size under the conditions of blasting penetration test,and the following conclusions and achievements:(1)The energy generated by the charge blasting at the junction of the coal and the rock creates abundant fissures for the coal and rock mass,which enhances the gas permeability of the coal seam.On the one hand protect the control holes in the bottom rock formation for later gas extraction.On the other hand the fissures in the slab formations provide space for cracks and displacements in soft coal seams,effectively reducing the closure of fissures and providing a stable gas flow path.(2)With the control hole diameter increases,the effect of the guide hole on the fracture is more obvious.The smaller the blasting cavity,the smaller the deflection angle of the fracture through the boundary of the model,and reduces the relative stress concentration when the bore diameter increases to a certain extent,which makes the fissure appear obvious mesh distribution.(3)In the case of large control holes,due to the provision of adequate free surface blasting energy in the role of coal to nroduce blast holes along the center to the surrounding squeeze coal deformation of mobile-based micro-cracks,making coal has an angle of 8° from periphery to the center of the model.(4)By blasting in coal and rock mass at the junction,the stress wave propagates to the weak boundary of the coal seam,forming multiple reflection superposition,and this repeated stretching superposition acts on the coal body to cause more displacement and destruction of the coal body.(5)The numerical simulation results show that as the control hole increases,the fissures in the coal and rock mass become more and more abundant,and the displacement and mutual intrusion of coal and rock mass are larger and the energy loss in the blasting cavity is higher.The smaller the cavity,when the control hole reaches a certain degree continues to increase,due to the control hole to provide a large free surface,making the coal under the blasting action produced a more obvious movement of the area in the vicinity of the control hole damage,and the fissures in the rock mass form a three-dimensional fissure structure in the cracks in the coal body.The stable control hole in the rock mass is the subsequent gas drainage and provides a long-term and efficient protection.(6)Industrial test using floor through-seam borehole of coal and rock at the junction of charge blasting to increase the gas concentration and pure flow,increased gas permeability,effective drainage radius of 6m,eliminating the danger of rock cross-cut coal uncovering gas outburst.