## 2 Physical and Mechanical Properties of Rock Mass Under THMC Coupling
### Overview of Multi-Field Coupled Rock-Deformation Studies
However, earlier research primarily focused on hydraulic coupling effects, leaving gaps in understanding how high-gradient temperature fields influence the mechanical characteristics and distortion behavior of surrounding rock masses (Figure 3) [135]. One pressing challenge in this area of research is improving THM models to more accurately reflect the post-peak behavior of brittle rocks, especially in terms of how strength declines after failure. Such improvements are essential for better predicting rock behavior in the long term, particularly under the extreme conditions found in deep engineering environments. The importance of multi-field coupling research becomes starkly evident in the context of engineering disasters, such as slope instability in landfills. Under the combined effects of THMC processes, these instabilities can result in catastrophic consequences. For example, Figure 4 highlights how multi-field coupling effects can lead to landfill slope failure. Such disasters underscore the critical need for comprehensive research to understand and mitigate these risks. A deeper investigation into the catastrophic processes that occur in landfills due to multi-field coupling can help prevent the fugitive release of pollutants and other hazardous outcomes. Figure 2: THMD coupling mode [133]. The study of rock deformation under the influence of THMC multi-field coupling is fundamentally rooted in understanding the geological conditions and environmental stresses that act on rock masses. By integrating laboratory experiments, theoretical analysis, and numerical simulations, researchers aim to uncover the mechanisms of deformation and failure, as well as the damage evolution of rocks subjected to multi-field coupling. This area of research is inherently interdisciplinary, combining principles from geology, damage mechanics, solid mechanics, fluid mechanics [99; 122], and chemistry to offer a more complete understanding of rock mass behavior under complex conditions. When examining rock masses subjected to multi-field coupling, particularly in challenging environments, they are referred to as complex rock masses. Figure 5 illustrates this concept, highlighting the intricate interactions between various fields in fractured rock masses. To describe the overall deterioration of these masses, researchers study the deformation and failure mechanisms under the influence of coupled physical fields. This comprehensive approach not only helps in predicting rock behavior but also provides practical insights for applications in mining, civil engineering, and environmental management. Figure 4: Schematic illustration of (**a**) the attribution of THMC coupling and (**b**) THMC behavior for landfill catastrophe process. Figure 3: Schematic sketch of in situ stress on the tunnel with peak ground temperature [135]. [PERSON] et al. [136] conducted triaxial creep tests to assess rock mass aging characteristics, estimating dynamic constitutive creep model parameters based on test data. [PERSON] et al. [137] investigated shale creep under high confining pressure and varying temperatures, finding increased creep strain with higher temperatures, axial differential stress, and reduced confining pressure. [PERSON] and [PERSON] [138] modified a torsional ring-shear device to examine cohesive soil's residual-state creep, producing a predictive creep failure curve for landslide displacement. [PERSON] et al. [139] developed a micromechanical model simulating brittle rock creep under triaxial stress. Lastly, [PERSON] et al. [140] introduced a nonlinear damage creep constitutive model for high-stress soft rock to explore its creep deformation, contributing valuable insights for underground engineering support design.