液氮半溶浸煤裂隙扩展试验研究

Experimental investigation on fracture extension of coal semi-submitted by liquid nitrogen

为分析液氮半溶浸作用下不同饱水度煤裂隙扩展特征,取山西无烟煤原煤煤样,利用自制的液氮半溶浸试验装置对不同饱水度煤样开展了半溶浸试验研究,测试了液氮作用前后煤样波速变化和表面微裂隙宽度扩展情况,结果表明:煤样的饱水度对液氮冷冻煤作用效果影响很大,饱和煤样波速改变率和裂隙宽度扩展率最大,半饱和煤样次之,干燥煤样最小;越靠近液氮作用面,煤样温度变化越大,液氮作用效果越显著,液氮溶浸煤样的波速变化率和裂隙宽度扩展率都最大;饱和、半饱和煤样微裂隙扩展的主要原因是水相变为冰引起的冻胀力,干燥煤样微裂隙扩展的主要原因是温度梯度引起的温度应力。

To investigate the extension characteristics of coal samples semi-submitted by liquid nitrogen with different water saturation,the anthracitic coal samples from Shanxi province were semi-submitted in liquid nitrogen with the selfmade experimental setup.The ultrasonic velocity change and the cracks＇ width extension of coal samples subjected to liquid nitrogen were tested.The results show,first,the saturation of coal samples has great effects on the cracks ＇ extension subjected to liquid nitrogen,the ultrasonic velocity change and the cracks＇ width extension of the saturated coal samples are maximum,those of the semi-saturation coal samples become worse,those of dry coal samples are worst; second,the nearer to the surface of the liquid nitrogen,the greater the temperature change of coal samples is,and there is much more significant effect of liquid nitrogen; third,the main reason of the cracks＇ extension of the saturating and semi-saturation coal samples is the frost heave pressure caused by the phase from water to ice,thermal stress due to temperature gradient induces the cracks＇ extension of dry coal samples.