Experimental study on technology of permeability enhancement with dry-expansion cracking in high-gas coal seam

Gas extraction is the key to gas disaster control in coal mines, the structural transformation of coal seam is the core of gas extraction, dry-expansion cracking is an effective way to realize the structural transformation of coal seam.This paper proposes a technology of dry-expansion cracking to increase permeability.Using a self-made test system of dry-expansion cracking.And low density foamed concrete is used to simulate coal-rock mass.the physical test of dry-expansion cracking was carried out, we get the law and effect of cracking under two conditions.One is with confining pressure; the other is no confining pressure.The results show that under the condition of no confining pressure, the cracking pressure of concrete specimen is 2.04-3.17 MPa.It shows diametral tensile failure, and there are two kinds of crack shapes.One is two symmetrical through cracks with the expansion tube as the center; the other is three cracks with the expansion tube as the center, the included angle is about 120°, and the cracking time is about 10-40 s.Under the condition of confining pressure, the damage degree of concrete specimens increases.The cracking pressure is 4.50-6.78 MPa, it produces three main cracks and eight to fourteen secondary cracks.The cracking time is about 30-400 s.The main crack propagates along the direction of the maximum principal stress.And after the macro cracks are formed, the secondary cracks can be further promoted by increasing the cracking pressure.The power of dry-expansion cracking technology is concentrated, it has several load types and sufficient fracture development.Coal seam structure has been effectively transformed.It can provide a new technology and theoretical support for the structural transformation of coal seam.