Modelling of gas-driven fracturing and fragmentation in liquid CO2 blasting using finite-discrete element method

The high-pressure gas combined with the action of the stress wave has a significant effect to drive fractures and enhance fragmentation in CO2 blasting. Modelling the whole process considering the gas penetration is of great importance for understanding the rock-breaking mechanism in CO2 blasting. In this study, a new method capable to simulate the gas pressurization in cracks is implemented based on the framework of the combined finite-discrete element method. The micro parameters are calibrated against the uniaxial compression test and Brazilian disc test. Two primary scenarios are set to mimic CO2 blasting: scenario one, only a time-varying pressure is applied on the borehole wall assuming that all the gas bursts out to the atmosphere; scenario two, both the stress wave and gas pressure are considered assuming that the gas penetrates into cracks. Moreover, different peak pressures corresponding to different kinds of fracturing devices are simulated in each scenario. The results indicated that: (a) gas pressurization can greatly increase the range of the fracture zone and the count of cracks, and plays a dominant role in rock breakage; (b) gas pressurization reduces the average size of fragments and increase the fractal dimension of the debris distribution; (c) gas pressurization increases the peak particle velocity (PPV) at different distances, causes more serious vibration disaster and reduce the attenuation coefficient.