温度冲击下煤体裂隙结构演化的显微CT实验研究

Experimental research on cracking process of coal under temperature variation with industrial micro-CT

为研究温度冲击下煤体裂隙结构演化特征,以期从微细观方面揭示煤体对温度的响应机制。采用SLX–80型高低温实验系统对原煤进行4种温差条件下的冷热冲击实验,利用工业显微CT系统对温度冲击前后的煤样进行扫描和裂隙结构的三维立体重建,基于VGStudio MAX图像分析系统建立煤样清晰的裂隙可视模型,并对煤体裂隙结构演化特征进行量化表征,运用非定常热应力理论分析温度冲击下的破煤机制。研究结果表明:温度冲击促使煤体内部裂隙扩展加宽,萌生新裂隙,裂隙体积、壁厚、表面积均与温差呈正相关关系,不同温差产生的热应力决定了煤样的损伤程度;温度冲击过程中产生了大量的声发射信号,声发射信号的产生主要集中在前600 s,且温差越大所产生的声发射能量越高;温度冲击所产生的最大热应力位于煤样表面的切向方向,热应力超过煤样抗拉强度是导致裂隙萌生、扩展和相互贯通的直接原因。研究结果可为煤层气高效开发和提高煤层瓦斯抽采率提供技术支撑。

The mechanism and characteristics of coal cracking under temperature shock was studied with micro-CT. The high-low temperature test system SLX–80 was used to exert the cold and heat shock on the raw coal with four temperature differences designated. The industrial micro-CT system was used to scan the coal samples before and after the temperature shock so that three-dimensional fracture structure of coal samples may be reconstructed with the image analysis system VG Studio MAX. The characteristics of cracking process were described quantitatively. The transient thermal stress theory was used to analyze the coal breaking mechanism under temperature shock. The results show that the temperature shock promotes the expansion and widening of cracks within the coal body and initiates new cracks. The crack volume,wall thickness and surface area are all positively correlated with the temperature difference,indicating that the thermal stress generated by different temperature differences determines the degree of damage of coal samples. A large number of acoustic emission signals were generated in the process of temperature shock and mainly concentrated in the first 600 s. The greater the temperature difference is,the higher the acoustic emission energy. The maximum thermal stress generated is tangential to the coal surface. The thermal stress exceeding the tensile strength of coal samples cause directly the initiation,propagation,and interpenetration of fissures.