The influence of moisture on the frost heave characteristics of gas-containing coal

Refrigeration technology provides a new method for preventing coal and gas protrusions. In this study, the freeze-thaw characteristics of gas-containing coal under various moisture conditions (0%–20%) were investigated through experiments conducted on an independently constructed freeze-thaw simulation platform for gas-containing coal. The results mainly include: 1) The cooling curves of externally watered coal samples exhibit four stages: rapid cooling, constant phase change, slow cooling and final constant temperature. The dry coal samples showed only rapid cooling, followed by temperature stabilization. 2) Freezing deformation occurred only when the moisture content exceeded 8%, and a “hysteresis” effect appeared in its temperature and deformation. 3) Under the same humidity conditions, the gas-containing coals produced significantly greater freezing strain than the non-gas-containing coals. The duration of the freeze-up deformation increases linearly with the increase in moisture content; the duration of the gas-containing coal is longer. 4) The residual strain after freeze-up is in a logarithmic function relationship with the moisture content. The freezing and expansion forces destroyed the pore structure, connecting medium-sized pores into large pores, and simultaneously generated new micropores, resulting in a significant increase in the proportion of large pores. These results indicate that moisture, temperature, and gas presence synergistically control the freeze-up deformation characteristics of coal, providing important insights into the application of freezing technology to coal and the intrinsic mechanisms of gas outbreak prevention.