Study on the evolution law of hole cracks in deep iron ore under microwave-assisted blasting

With the continuous deepening of China 's deep strategy, a new situation has been opened for the expansion of resource development to the deep. At the same time, it also needs to face more complex engineering problems, such as high ground stress, high strength rock mass and other geological conditions. In order to solve the problems of low efficiency and high energy consumption of traditional blasting in deep rock mass, a new method of microwave-assisted blasting rock breaking is proposed. In this paper, the coupling test of microwave radiation and single-hole blasting in simulated deep environment is carried out with magnetite as the research object. Based on the analysis of the test results, combined with X-ray high-precision micro-CT scanning and three-dimensional reconstruction technology, the changes of pore volume, surface area, fractal dimension, pore structure and crack propagation under different loading conditions are analyzed, and the influence of different loading conditions on the evolution of pore and fracture structure of iron ore is discussed. The research shows that : (1) Microwave radiation promotes the development and initiation of pores and fissures. With the increase of microwave damage, the volume, surface area and fractal dimension of pore fracture distribution complexity of iron ore after blasting show a gradual upward trend. Compared with prolonging the irradiation time, increasing the microwave power has a more significant effect on the development of pore fracture of iron ore. When high power microwave radiation is used, the increase of pore volume and surface area of the sample reaches the maximum of 30.48 % and 31.37 %, respectively. (2) Microwave radiation can effectively improve the blasting effect, which can be attributed to the connection and penetration of pores and microcracks, providing more channels for blasting stress wave propagation. The peak of the distribution curve of pore radius and throat length of the sample gradually shifts to the direction of larger radius and longer length with the increase of microwave damage, and the distribution range of pore coordination number increases.(3) The confining pressure inhibits the synergistic effect of microwave-blasting. With the increase of confining pressure, the crack propagation is obviously limited, the volume and maximum length of the through-hole cracks are significantly reduced, and the volume ratio of the isolated hole cracks is increased. The confining pressure changes the propagation direction of the main crack, and the propagation direction of the main crack is changed from the radial shape without confining pressure to the direction of the maximum principal stress. This study provides a reference for the engineering application of microwave-assisted blasting technology in deep high stress environment.