Experimental Study on Key Parameters of Pulsating Water Injection for Coal Seam Damage

Coal mine dust is one of the most severe hazards that threaten underground coal mining, and it can be effectively controlled and prevented by coal seam water injection. However, with the progress of coal mining, the excavation advances to the deep horizontal levels, where the coal seam porosity is smaller due to the increased crustal stress. The static pressure coal seam water injection becomes insufficient for dust control, which has urged the development of pulsating water injection that can realize coal seam damage and wetting simultaneously by the pressure pulse effect. In the present study, the damage law of coal seam caused by pulsating water injection was explored experimentally using a triaxial pulsating seepage device and taking the Wudong coal mine in Xinjiang, China, as the research background. The following conclusions have been obtained. ① Pulsating water injection can effectively damage the coal seam, increase its permeability coefficient, and promote its wetting effect. ② The permeability coefficients of coal treated with pulsating water injection in different pulse waveforms are in the order of rectangular waveform > sinusoidal waveform = triangular waveform > constant pressure under the lower and upper pressure limits of 5-8 MPa, in the order of sinusoidal waveform > rectangular waveform > triangular waveform > constant pressure under the lower and upper pressure limits of 4-9 MPa, and in the order of sinusoidal waveform > rectangular waveform = triangular waveform > constant pressure under the lower and upper pressure limits of 3-10 MPa. ③ Under the experimental variable conditions of this study, the optimal pulsating water injection parameter is determined to be a sine waveform, the upper pressure limit is 10 MPa, and the lower limit is 3 MPa. ④ The optical microscopy and scanning electron microscopy imaging of the coal sample before and after water injection verifies that pulsating water injection can damage the coal seam, expand its pores and fractures, and enhance its wetting effect.