饱水度和再溶浸对液氮冷冻煤致裂的影响

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

  • 摘要: 为解饱水度和液氮再溶浸对液氮冷冻煤致裂效果的影响,取王营子矿的干燥、天然含水和饱水3组原煤煤样在室内实验室开展了液氮溶浸实验,测试液氮溶浸前后煤样波速变化,观察煤样表面裂隙发展。定义了煤样波速变化率和代表性裂隙面积变化率2个指标,分析了饱水程度、液氮再溶浸对煤内原生裂隙结构扩展和新裂隙萌生的影响,结果表明:① 在液氮作用下,原煤内主要发生原生裂隙扩展及新裂隙萌生。② 煤的饱水程度对液氮溶浸煤致裂效果影响很大。随着饱水度增加,煤样的波速变化率和代表性裂隙面积变化率都增加。饱水煤样的波速变化率和代表性裂隙面积变化率分别为干燥煤样的21.2倍和11.7倍。③ 液氮再溶浸作用将加剧煤样内缺陷结构发育,提高液氮作用效果。天然含水煤样的液氮再溶浸作用效果更好。

     

    Abstract: 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.

     

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