Effects of saturation and re-submersion on coal fracturing subjected to liquid nitrogen shock

In order to obtain the effect laws of saturation and re-submersion on coal fracturing subjected to liquid nitrogen shock, the liquid nitrogen submersion tests for three groups including dried, natural water content and saturated coal samples obtained from Wangyingzi Mine were performed.The changes of wave velocity and crack's area of the coal sample in initial state and after being cooled in liquid nitrogen were tested.The two parameters including the change rates of the wave velocity and typical crack's area were defined and adopted to study the effects of water content and re-submersion on the extension of the oiginal cracks and cracks's propagation.The main conclusions are:① Under thermal shock by liquid nitrogen, there appear the extension of initial cracks and new cracks' propagation in natural coal.② There exist great effects of water content on fracturing coal subjected to liquid nitrogen submersion.With the increase of water content, the change rates of the wave velocity and typical crack's area also increase.The change rates of the wave velocity and typical crack's area of saturated coal sample are 21.2 and 11.7 times than those of dried coal samples, respectively.③ The re-submersion of liquid nitrogen will lead to much more cracks, and improve the effects of liquid nitrogen.Coal samples with natural water content subjected to re-submersion are much more fractured.