Study on influence mechanism of liquid nitrogen to permeability improvedfunction of water bearing coal and rock mass

In order to study the action mechanism of the liquid nitrogen to the water bearing coal and rock, a self developed self pressurized liquid nitrogen cold immersion device was applied to the liquid nitrogen cold immersion test on the coal samples with different water bearing saturation and a comparison analysis was conducted on the permeability variation law and micropore, pore development condition of the coal samples before and after the liquid nitrogen cold immersion. From a view of the theory, the paper had an explanation on the damage mechanism of the water bearing coal samples by the liquid nitrogen cold immersion. The results showed that after the liquid nitrogen cold immersion, the permeability of the coal samples would be increased with the water bearing saturation increased. The increased amplitude would be in an index type increasing and the increased amplitude was ranging from 70.6% to 1 254.9%. Under the saturation condition of the coal samples, the liquid nitrogen affected to the coal and rock would be the water-ice phase change to make the volume expansion mainly. The failure degree of the micro-structure would be higher than the dry coal samples. The coal sample would have the pore extension, pore widening and other phenomenon and the permeability effect would be better.