低温作用下煤体细观结构变化及相变致裂实验研究

为了研究低温作用下煤体细观结构演化规律，采用CT扫描不同冻结温度下干燥和饱水煤样细观结构图像，构建三维可视化裂隙模型，探究冻结煤体裂隙演化机理。研究结果表明:随着温度的降低，煤样内部产生的拉应力逐渐增大，加之，冰水相变产生冻胀力，导致煤样内部裂隙网格不断扩展演化；冰水相变产生的冻胀力是饱水煤样和干燥煤样裂隙演化具有差异性的原因，孔隙、裂隙水冰点随着孔隙、裂隙的半径减小而逐渐下降，从而导致壁厚较大的裂隙中水分先行冻结，随着温度的继续降低，壁厚较小的裂隙中水分才发生冻结。

Experimental study on meso structure change and phase transforming fracturing of coal under low temperature

In order to study the evolution laws of meso-structure in coal under low temperature effect,the meso-structure images of dry and saturated coal samples under different freezing temperatures were scanned by using CT,then a three-dimensional visual fracture model was constructed,and the evolution mechanism of fractures in the frozen coal was explored.The results showed that the tensile stress generated in the coal sample increased gradually with the decrease of temperature,in addition,the frost heaving force was produced by the phase transformation of ice-water,which induced the constant extension and evolution of fracture grid in the coal sample.The frost heaving force produced by the phase transformation of ice-water was the reason for the difference of fracture evolution between saturated coal sample and dry coal sample.The freezing points of pore water and fissure water decreased gradually with the decrease of the radii of pore and fissure,which resulted in the advance freezing of water in the fissure with large wall thickness,then the water in the fissure with small wall thickness froze along with the follow-up decrease of temperature.