Mechanical Properties and Fracture Evolution Characteristics of Raw Coal under Different Confining Pressures

The triaxial compression tests of raw coal under different confining pressures were carried out by the industrial CT scanning system of coal and rock under load to investigate the mechanical properties and damage characteristics of raw coal under different confining pressures, the CT scanning information of the whole process of destabilization and damage of raw coal was obtained by combining with its own CT scanning system, and the evolution law of crack propagation of raw coal under different confining pressures was analyzed. The results show that: (1) With the increase of confining pressure, the overall bias stress-strain curve shifts to the right, the peak strength increases linearly, while the peak strain and elastic modulus both increase as a quadratic function, and the peak strength increases by the largest amount; (2) Based on the CT scan images, the fracture evolution characteristics inside the coal sample can be divided into four stages: fracture pressure density slowly decreasing stage, fracture sprouting stable development stage, fracture rapid increase stage, fracture expansion through stage, and with the increase of confining pressure, the fracture density gradually decreases; (3) Under triaxial loading, the damage of raw coal is mainly in the form of shear damage, with the size of the breaking angle ranging from 20° to 40°, and with the increase of confining pressure, the breaking angle increases as a quadratic function. The research results have certain reference significance for underground roadway, stope support design, surrounding rock stability judgment and mine disaster and accident prevention.