Experimental Study of Prefabricated Crack Propagation in Coal Briquettes under the Action of a CO2 Gas Explosion.

Abstract

CO2 deep-hole presplit explosions are an important technology for enhancing gas drainage in low-permeability coal seams. In the process of a CO2 gas explosion, the initial burst crack generated by the shock wave expands the crack tip under the splitting action of high-pressure CO2 gas. To explore the effects of CO2 gas explosions on crack tips, we constructed an analytical model of gas pressure attenuation at different positions based on fluid motion equations, proposed equations for crack opening and growth rates, and inverted the energy field of the whole process of CO2 blasting. We used a test platform for the independent development of CO2 gas explosions under experimental conditions of 1 MPa axial pressure and 2 MPa CO2 gas pressure and a VIC-3D measurement system. We conducted the gas explosion experiments on prefabricated cracked samples with a crack length of 10 mm and width of 0.2 mm to analyze the dynamic response of the crack tip. The results showed that there were three stages in the propagation of a prefabricated crack under the action of a CO2 gas explosion. The first stage, from 0 to 290 ms, included energy storage at the crack tip and a maximum opening rate increment of 0.0043 m/s. The second stage, from 291 to 295 ms, was rapid crack propagation with maximum opening rate increment and propagation rates of 0.1865 and 5.35 m/s, respectively. In the third stage, from 296 to 309 ms, the crack tip propagated slowly, the maximum opening rate increment and growth rates were 0.0969 and 5.81 m/s, respectively, and the crack arrest coordinates were 4.57 and 35.28 mm. The experimental study verified the accuracy of the calculation model, proved that CO2 gas promotes the growth of crack tips, explained the spatiotemporal evolution mechanism of the CO2 explosion process, and provided experimental support for subsequent research related to explosions.