Water-immersion softening mechanism of coal rock mass based on split Hopkinson pressure bar experiment

The coal mining process is affected by various water sources such as groundwater and coal seam water injection. Understanding the dynamic mechanical parameters of water-immersed coal is helpful for coalmine safe production. The impact compression tests were performed on coal with different moisture contents by using the ϕ 50 mm Split Hopkinson Pressure Bar (SHPB) experimental system, and the dynamic characteristics and energy loss laws of water-immersed coal with different compositions and water contents were analyzed. Through analysis and discussion, it is found that: (1) When the moisture content of the coal sample is 0%, 30%, 60%, the stress, strain rate and energy first increase and then decrease with time. (2) When the moisture content of the coal sample increases from 30% to 60%, the stress “plateau” of the coal sample becomes more obvious, resulting in an increase in the compressive stress stage and a decrease in the expansion stress stage. (3) The increase of moisture content of the coal sample will affect its impact deformation and failure mode. When the moisture content is 60%, the incident rod end and the transmission rod end of the coal sample will have obvious compression failure, and the middle part of the coal sample will also experience expansion and deformation. (4) The coal composition ratio suitable for the coal immersion softening impact experiment is optimized.