Damage evolution characteristics of 3D-reconstructed coal during loading and its size effects based on CT scanning

Coal is a porous material containing pore structures and mineral components, exhibiting pronounced anisotropy and size effects. In order to investigate the influence of coal anisotropy and size effects on its failure characteristics, this paper proposes a simulation method for characterizing and reconstructing three-dimensionally the internal pores and mineral components of coal samples based on CT scanning, nuclear magnetic resonance, and X-ray diffraction. Specifically, we obtained simulation parameters of three-dimensional reconstruction models of coal matrix and mineral components through inverse laboratory uniaxial compression experiments, while simulated and analyzed the strength damage characteristics of coal bodies with different aspect ratios. The simulation results show that: ① During the loading process, the plastic zone first gradually expands and connects outward around the pores and mineral components. In terms of spatial distribution, the plastic zone expands vertically from the loading end to the interior in the early stage, and in the later stage, it expands horizontally from the surroundings to the interior. After the model is damaged, a "double truncated cone structure" is formed in the non-plastic zone. ② The increase of aspect ratio leads to an increase in the compressive strength(p) of coal samples, the strain(ζ) at yielding strength, and the elastic modulus(K), among which ζ and K increase linearly, while the margin of increase in p gradually decreases. ③ The total energy and elastic energy of coal sample loading increase exponentially, while the dissipated energy increases linearly. The increase of aspect ratio leads to an increase both in the accumulated elastic energy in the coal body and in the released energy during failure, which easily induce dynamic impact-related disasters. This study provide references for the reasonable selection of coal pillar size in impact mine pressure area.