Liquid carbon dioxide blasting technology as a new environmentally safe rock cracking technology has been widely used in mining, enhancing the permeability of coal seam, road construction, and other fields. In this study, a liquid carbon dioxide blasting experiment was conducted on a concrete specimen of size 500mm×500mm×400 mm firstly, and the crack distribution and blast hole morphology were observed. Then, the peridynamics model of rock fracturing under liquid carbon dioxide blasting was established, and the crack propagation in liquid carbon dioxide blasting and the influence of explosion pressure and numbers and radii of releasing holes on the liquid carbon dioxide blasting effects were analyzed. The results showed that the broken concrete specimen had no obvious smash district and the direction of crack propagation was perpendicular to that of carbon dioxide release after liquid carbon dioxide blasting. The failure of the specimen was only caused by the blasting stress wave, and the quasi-static effect of high-pressure carbon dioxide did not have sufficient time to play its role. With an increase in the stress wave strength and the numbers and radii of releasing holes, the fracturing velocity of liquid carbon blasting will increase. The cracks produced by liquid carbon dioxide blasting were mainly distributed in the middle of the adjacent releasing holes. The research results had a good guiding significance for understanding the mechanism of liquid carbon dioxide rock breaking and optimizing and improving the liquid carbon dioxide fracturing device.

The technique of breaking rocks using carbon dioxide phase transition technology is being widely applied in current research. This article combines theoretical and practical methods to analyze the mechanism by which high-pressure gas breaks rock at different stages. Using the observation that liquid carbon dioxide forms a high-pressure jet from release holes at the moment of release, a formula for calculating the initial pressure on the wall in the direction of release was obtained, and the pattern of initial crack formation on the borehole wall under different initial stress conditions was examined. An experiment using carbon dioxide phase transition technology to fracture rock without an initial stress field was conducted. The mechanism of generation and expansion of subsequent cracks under stress waves and high-pressure gas was analyzed, and the formula for calculating crack propagation radius under stress waves was obtained. The results suggested that under the quasi-static action of high-pressure gas, cracks begin to develop when the stress intensity factor K_I at the crack tip is equal to or greater than the fracture toughness K_IC of the rock.

Micro-pore structure has a decisive effect on the physical and mechanical properties of porous materials. To further improve the composition of rock-like materials, the internal relationship between microscopic characteristics (porosity, pore size distribution) and macroscopic mechanical properties of materials needs to be studied. This study selects portland cement, quartz sand, silica fume, and water-reducing agent as raw materials to simulate sandstone. Based on the Nuclear magnetic resonance (NMR) theory and fractal theory, the study explores the internal relationship between pore structure and mechanical properties of sandstone-like materials, building a compressive strength prediction model by adopting the proportion of macropores and the dimension of macropore pore size as dependent variables. Test results show that internal pores of the material are mainly macropores, and micropores account for the least. The aperture fractal dimension, the correlation coefficient of mesopores and macropores are quite different from those of micropores. Fractal characteristics of mesopores and macropores are obvious. The macropore pore volume ratio has a good linear correlation with fractal dimension and strength, and it has a higher correlation coefficient with pore volume ratio, pore fractal dimension and other variable factors. The compressive strength increases with the growth of pore size fractal dimension, but decreases with the growth of macropore pore volume ratio. The strength prediction model has a high correlation coefficient, credibility and prediction accuracy, and the predicted strength is basically close to the measured strength.