## 5 Discussion  
By comparing the mechanical responses of fractured rock masses with and without infill under various freeze-thaw cycles, it was found that the infilling material plays a dominant role in strength degradation during the initial stages of freeze-thaw processes. After two freeze-thaw cycles, the influence of the infilling material on the internal friction angle and cohesion at a burial depth of 5.27 m reached 99.41% and 89.32%, respectively (see Figures 12 and 13). This indicates that shallow rock masses are more susceptible to shear failure during early freeze-thaw stages due to the mechanical weakness of the infilling, leading to significant degradation of strength parameters.  
As the number of freeze-thaw cycles increases, the strength of the infill tends to stabilize, and its softening effect gradually weakens. In contrast, the homogeneous degradation of the intact rock matrix becomes more pronounced, ultimately dominating the strength evolution at later stages. This process reveals a staged control mechanism of freeze-thaw effects on structural planes: the early-stage degradation is governed by infill-induced damage, while the later-stage strength loss is primarily driven by the propagation of microcracks within the intact rock blocks.  
Figure 12: Variation in the contribution of intact rock and infilling material to the degradation of rock mass mechanical properties with increasing freeze–thaw cycles at different burial depths: (**a**) internal friction angle; (**b**) cohesion.  
The above patterns are consistent with the coupled evolution trend of mechanical parameters under freeze-thaw cycles and burial depth established in Chapter 4. Furthermore, they provide a theoretical explanation for the rapid decrease in safety factors observed in shallow slope zones, thereby validating the critical role of infilling layers in the slope failure mechanism.  
This study was conducted based on the geological conditions of a specific open-pit site, and the degradation parameters obtained are site-dependent. Nevertheless, the modeling framework, parameter calibration methodology, and predictive approach developed herein are generalizable. They can be applied to other cold-region slopes with similar lithological and hydrothermal conditions. To extend applicability, future studies should incorporate site-specific climatic, geological, and hydrogeological data for model calibration and validation.  
The COMSOL model developed in this study adopts a continuous medium assumption and does not explicitly simulate the discrete characteristics of fracture geometry and block structure. The influence of fractures is incorporated through equivalent strength reduction factors, which are suitable for evaluating large-scale overall slope stability. In addition, the current model is based on partially saturated conditions and does not account for mechanisms such as capillary rise and rapid pore pressure buildup during thawing. It is recommended that future work employ a DFN-THM (Discrete Fracture Network--Thermo-Hydro-Mechanical) coupled framework to construct a more realistic, multi-scale, and multiphysics simulation system, enabling a more accurate representation of potential failure mechanisms.