Study on coal crack propagation and failure mode with different moisture content under uniaxial compression

In order to study the influence of moisture intrusion on crack propagation and failure mode of loaded coal, uniaxial compression tests and acoustic emission monitoring of coal with different moisture contents are carried out. The stress-strain characteristics, macroscopic failure patterns and change law of cumulative ringing counts of loaded coal with different moisture contents are compared and analyzed. The results of uniaxial compression tests show that with the increase of moisture content, the uniaxial compressive strength and elastic modulus of coal decrease continuously. The stress drop rate of coal gradually slows down in the post-peak stage. The macroscopic failure mode of coal samples changes from typical brittle failure to shear-tension combined failure. The acoustic emission monitoring results show that the cumulative ringing counts decreases with the increase of coal moisture content. The cumulative ringing counts curve's slope increases correspondingly, indicating that moisture intrusion can reduce the energy release when the coal cracks develop. However, the moisture intrusion aggravates the internal structure damage of coal. The results show that the water intrusion weakens the friction between crystal particles on the surface of cracks to some extent, and increases the possibility of coal sliding failure. At the same time, the water intrusion also reduces the surface active energy of the coal, resulting in a significant increase in the number of cracks generated during the loading process of the coal sample. This leads to a large drop in the macroscopic mechanical strength of the coal.