Study on damage characteristics of coal under uniaxial compression based on Micro-CT and DVC

The study of the damage process of coal is essential to understand the changes of their mechanical behaviour and permeability properties. X-ray computed tomography(CT) was used to scan the coal rock in situ under uniaxial compression conditions. Combining the digital core technology and digital volume correlation method (DVC), the deformation displacement field and strain field of the coal rock were calculated. The fracture development and evolution law, the relationship between the dynamic evolution of coal rock damage and the permeability performance were analyzed. It is found that under uniaxial loading, the damage of the coal rock is caused by a combination of axial force and the development of adjacent fractures, resulting in the development of internal fractures and the phenomenon of fracture compaction. In addition, the minerals in the coal play a guiding role in fracture development, and the fractrue development are closely related to the shape and distribution of minerals. The DVC analysis shows that the damage process of the coal is a dynamic evolutionary process, and the accumulation of deformation difference along different directions in each region leads to the occurrence of damage. The vector superposition of the displacement field reveals the deformation of the coal matrix in different directions, while the strain field shows the lateral expansion of the fracture under axial compression. During the loading process, the development of pore fracture in coal results in the increase of permeability properties, especially at the 1 100 N stage, where the permeability increased by 149.35 μm² and the maximum value of the damage variable D_\mathrmH was 8.2%. In addition, the number of connected pores and tortuosity τ were exponentially related to the damage variables. This study provides experimental data and theoretical support to deepen the understanding of the damage and permeability characteristics of coal.