Research on Mechanical Characteristics and Failure Mechanism of Coal-Rock Combined Bodies with Equal Strength

To investigate the distortion and damage properties of coal-rock combination (CRC) samples, the individual coal samples and rock samples and CRC were developed by similar materials with equal strength. Then, uniaxial compression (UC) tests and acoustic emission (AE) tests were performed on CRC samples with various rock-coal height ratios and loading rates. The strength, deformation, and AE properties of the CRC samples were analyzed to explore their failure mechanisms. The findings indicated that the individual coal samples and rock samples were mainly damaged by tensile splitting. For CRC samples, shear and tensile coupled failures were the main failure modes. Cracks are first generated from coal part and continue to expand to rock part. The coal-rock height ratio had little impact on the single AE event count peak value but had a certain influence on the cumulative number of AE event count. However, the loading rate had a large effect on the AE characteristics, and the strength and elastic modulus (E) of the CRC samples had linear or nonlinear increasing trend with increasing ratio of rock to coal height and loading rate. The research findings will have certain theoretical reference value for analyzing the mechanism of coal pillar failure.