This study designs and introduces an X-ray-compatible thermo-hydro-mechanical coupling triaxial device. The functional parameters of this device included a confining pressure, axial force, injected fluid pressure, and temperature up to 20 MPa, 400 kN, 10 MPa, and 100 °C, respectively. Triaxial stress loading–unloading cycles and permeability experiments for coal specimens were carried out using this device. Following four pre-set cycles, the specimen was scanned to identify internal cracks, and the relationship between stress, strain, permeability, and crack evolution was analysed. The experimental results showed that new cracks were mainly caused by the expansion of initial cracks as the triaxial stress cycles. The crack area fraction (CAF) increased almost linearly with the stress cycle. With the increase in CAF, the permeability of coal had increased under both high and low deviatoric stress. However, the increment of permeability that was driven by the CAF increment had decreased and eventually became stable. During the initial cracking stage, the increase in permeability from the CAF increase under high deviator stress was always greater. This demonstrates that the contribution of new cracks to increasing permeability under different triaxial stresses was significantly different. The outcomes from this study may provide benefits for coalbed methane extraction and dynamic hazard prevention.

本研究设计并介绍了一种兼容X射线的热-水-机械耦合三轴装置。该设备的功能参数包括围压，轴向力，注入的流体压力和分别高达20 MPa，400 kN，10 MPa和100°C的温度。使用该装置进行了煤样品的三轴应力装卸循环和渗透性实验。在四个预设循环之后，对样品进行扫描以识别内部裂纹，并分析应力，应变，渗透率和裂纹发展之间的关系。实验结果表明，新的裂纹主要是由于三轴应力循环中初始裂纹的扩展引起的。裂纹面积分数（CAF）随应力循环几乎线性增加。随着CAF的增加，高偏低应力下煤的渗透率均增加。但是，由CAF增量驱动的渗透率增量已减小，最终变得稳定。在初始开裂阶段，高偏斜应力下CAF渗透率的增加总是更大。这表明在不同的三轴应力下，新裂纹对增加渗透性的贡献是显着不同的。这项研究的结果可能为煤层气的提取和动态危害的预防提供益处。在高偏斜应力下，CAF增加的渗透率增加总是更大。这表明在不同的三轴应力下，新裂纹对增加渗透性的贡献是显着不同的。这项研究的结果可能为煤层气的提取和动态危害的预防提供益处。在高偏斜应力下，CAF增加的渗透率增加总是更大。这表明在不同的三轴应力下，新裂纹对增加渗透性的贡献是显着不同的。这项研究的结果可能为煤层气的提取和动态危害的预防提供益处。