Study on pressure relief and permeability enhancement effect of cutting coal seam with diamond-bead wire saw

In order to explore the pressure relief and permeability enhancement effect around coal seam slot cut by diamond-bead wire saw, firstly, the mechanical model of a doubly clamped roof beam based on the stress of the slot roof was established to analyze the force characteristics of the roof beam and the characteristics of the sinking contact bottom of slot roof (referred to as the contact bottom). Besides, the self-designed physical similarity simulation test platform was used to carry out various similar simulation tests to analyze the stress and displacement changes of coal and rock strata above and below the slot after cutting the seam using wire saw with different process parameters. Finally, based on the FLAC^3D numerical simulation and the development of a coal seam gas permeability calculation program, the distribution characteristics and periodic evolution laws of stress and permeability of coal and rock mass around the advancing slot of the coal working face were analyzed. The research shows that the wire saw cuts seams, which makes the stress around the slot redistribute, and the slot roof passes through three evolution forms of roof hanging, roof contact with the bottom, and continuous sinking with the advancement of the working face. When the roof does not touch the bottom, the upper and lower parts of the slot form a ‘U’-type pressure relief zone. The maximum deflection is at the center of the roof, which is also the first part to contact the bottom. After the roof contacts the bottom, the stress recovery occurs in the middle of the slot, which weakens the pressure relief and permeability enhancement effect of the slot. The larger the diameter of the diamond-bead wire saw is, the larger the ultimate span of the roof bottom is, the later the slot contacts the bottom, and the better the pressure relief effect is. With the same slot diameter, the second slot is added, and the pressure relief zone of the two slots is connected. The pressure relief effects promote each other, which weakens the stress recovery under the action of the two slots and increases the pressure relief range. When the slot advancing distance is long enough, due to the roof contacting the bottom, the pressure relief and permeability enhancement effect on both sides of the slot is better. The influence range of pressure relief is divided into stress concentration zone, pressure relief zone, stress recovery zone, pressure relief zone and stress concentration zone from left to right. The corresponding pressure relief zone and stress recovery zone have a better permeability enhancement effect.