Study on Loading Rate Dependence of the Coal Failure Process Based on Uniaxial Compression Test

Abstract

To study the influence of the loading rate on the failure process of coal, uniaxial compression tests were performed with various axial strain rates of 0.83 × 10–5 to 6.66 × 10–5 s−1 on coal samples, which were collected from the Shamushu Coal Mine in Sichuan Province. The parameters of stress, strain, and acoustic emission during the failure process were collected and recorded. The peak stress, axial strain stiffness, energy dissipation, and acoustic emission characteristics of coal samples with different axial strain rates were analysed. The results demonstrate that (1) as axial strain rates increase, the peak strength and degree of fragmentation of the coal sample after failure also increase, and they exhibit good dependence on the axial strain rate; (2) the axial strain rate has little influence on the change trend in strain stiffness during the process of failure, but as the axial strain rate increases, the strain stiffness value of the horizontal section of the axial strain stiffness curve increases, and the initial stress level of this stage has a forward trend; (3) as the axial strain rate increases, the total energy absorbed by the coal sample increases gradually, and the proportion of elastic strain energy decreases when the peak stress is reached, while the proportion of dissipated energy increases gradually; (4) as the axial strain rate increases, the AE signal’s activity increases in the process of sample failure, the threshold value of the strain level decreases corresponding to AE active and intense periods, and higher amplitude AE signals are produced in the violent period. The research results can provide reference for monitoring and controlling geological hazards, such as pillar instability and failure in underground mining.