An understanding of how the fracture permeability evolves in a coupled thermo-hydraulic-mechanical (THM) environment at real-time ultrahigh temperature has a great significance for many underground excavations. This paper designs a testing apparatus to take the effects of THM processes into account by coupling high temperatures and high triaxial stress. Correspondingly, the permeability evolution of fractured rock in the coupled THM environment under real-time ultrahigh temperature (20–650 °C) and triaxial stress (confining pressure of 5–25 MPa)/seepage pressure (0.5–6 MPa) conditions is studied. Then, using the X-ray micro-computed tomography technique, the evolution of the fracture aperture in the fractured rock subjected to various conditions is analyzed. The results indicate that for the coupled THM environment, the variations of the volumetric flow rate, nonlinear seepage parameters, and the fracture aperture of the fractured rock with the temperature and the triaxial stress are not straightforward, and the inflexion points of the curves happen at a confining pressure of 15 MPa and a temperature of 300 and 500 °C. Second, in the temperature range of 20–300 °C, in all the triaxial stress states, the volumetric flow rate and the fracture aperture decline slightly with an increase in the temperature due to the recoverable elastic compression on the propping asperities. However, in the temperature range of 300–650 °C (at a confining pressure equal to or lower than 15 MPa), the parameters rise slightly with an increase in the temperature due to the relatively large axial and lateral deformation of the semicylinders. Third, in temperature ranges of 500–650 °C (at a confining pressure equal to or lower than 15 MPa) and 300–650 °C (at a confining pressure higher than 15 MPa), the parameters rise sharply owing to the lateral fracturing of the semicylinders, so the variational trends are irregular. The findings of the current work can provide theoretical guidance on the assessment of the stability and compactness of high-temperature underground excavations.

了解裂缝渗透率在实时超高温下的热-水力-机械 (THM) 耦合环境中如何演变对许多地下开挖具有重要意义。本文设计了一种测试装置，通过耦合高温和高三轴应力来考虑 THM 过程的影响。相应地，研究了实时超高温（20-650 ℃）和三轴应力（围压5-25 MPa）/渗流压力（0.5-6 MPa）条件下THM耦合环境下裂隙岩石渗透率演化. 然后，利用X射线显微计算机断层扫描技术，分析了不同条件下裂隙岩石中裂隙孔径的演化。结果表明，对于耦合的 THM 环境，体积流量、非线性渗流参数、裂隙岩体裂缝孔径随温度和三轴应力的变化并不直接，曲线的拐点发生在围压为15 MPa、温度为300 和 500 °C。其次，在20-300°C的温度范围内，在所有三轴应力状态下，由于支撑粗糙体上的可恢复弹性压缩，体积流量和裂缝孔径随着温度的升高而略有下降。然而，在300-650°C的温度范围内（围压等于或低于15 MPa），由于半圆柱体的轴向和横向变形较大，参数随着温度的升高而略有上升。第三，在500～650℃（围压≤15MPa）和300～650℃（围压高于15MPa）的温度范围内，由于侧向压裂，参数急剧上升。半圆柱体，所以变化趋势是不规则的。目前工作的研究结果可为高温地下开挖的稳定性和密实性评估提供理论指导。