Study on Damage Characteristics of Deep Coal Based on Loading Rate Effect

In this paper, the uniaxial compression tests of coal under different loading rates are carried out by using the MTS rock mechanics loading system and the DS5 acoustic emission instrument, and the mechanical parameters and damage characteristics of coal samples under five loading rates are studied. The conclusions are as follows: The uniaxial compressive strength and the elastic modulus of the sample increase with the increase in the loading rate, whereas the strain at the peak point of stress decreases with the increase in the loading rate; at a low loading rate, the AE ring count of the coal samples is widely distributed, but the maximum AE ring count value is small. At a high loading rate, the AE ring count of the coal samples decreases, whereas the maximum AE ring count value increases significantly. With the increase in the loading rate, the maximum AE ring count and cumulative AE ring count of the sample increase. According to the damage variable curves of the coal samples under different loading rates, the damage evolution process of the samples before the stress peak is roughly divided into three stages: initial damage stage, stable damage development stage and rapid damage development stage. It is found that when the loading rate is low, the deformation time of the coal sample is relatively sufficient, whereas when the loading rate is high, the micro cracks have no time to develop and expand, the sample is destroyed instantly and the destruction of the coal sample is sudden. Therefore, with the increase in the loading rate, the damage variable value at the peak stress of the coal sample generally shows an increasing trend.