Granular coal crack propagation study under uniaxial compression based on J integral

Granular coal is a kind of multilayer and structured solid matter, which consists of a large assemblage of individual granular solids and has dual characters of coal and granular materials. Its crack propagation law can be studied using the coal mechanics and multi-scale characteristics. First of all, the linear elastic material may be damaged under compression; and the cause of crack propagation is explained from the viewpoint of energy that the dynamics of crack propagation is due to the release of strain energy. And then, further study on the granular coal crack propagation under uniaxial compression from macroscopic and microscopic raspects is carried out by physical experiment and numerical simulation. Results show that a cone is formed at the bottom of the heap, the crack propagation is slowed down with the decrease of coal particle size, mutation points in crack propagation will appear, and the crack will not be smooth after the granular coal is damaged completely. Besides, due to the influence of granular coal particle size, uniformity has an important effect on crack propagation. The greater the homogeneity coefficient, the later the fractures occur. The acoustic emission energy release becomes frequent and severe in the mild, moderate and deep stages of crack propagation. These results will be conducive to further study on the law of geotechnical granular materials crack propagation under compression.