## 5 Conclusions  
This study focuses on coarse-grained soil in the southeastern Xizangan region. Through indoor FT cycle tests and triaxial shear tests, the mechanical property evolution of coarse-grained soil under FT cycles at different moisture contents is systematically analyzed. Additionally, a slope stability analysis model is constructed based on COMSOL Multiphysics software. The following conclusions are drawn:  
1. FT cycles significantly degrade the mechanical properties of coarse-grained soil in southeastern Xizang. The stress-strain curve of the samples initially shows a higher slope and stable peak value. After one FT cycle, the peak stress decreases by 8.4%, and after fifteen cycles, the overall reduction reaches approximately 31.2%. The cohesion and internal friction angle decrease by an average of 26.5 kPa (38-55%) and about 7.4\({}^{\circ}\) (29-32%), respectively, with changes stabilizing after 10 cycles. 2. An increase in moisture content leads to an increase in pore water pressure, weakening the particle interlocking effect. As the moisture content increases from 7.6% to 11.6%, the strain softening degree increases from 8.0% to 16.0% in the non-FT samples, and after FT cycles, it increases further to 27.9-33.7%. This indicates that the shear strength degradation is more pronounced at higher moisture levels. 3. Increased confining pressure significantly enhances shear strength. Under conditions where the confining pressure increases from 50 kPa to 200 kPa, the peak stress increases by as much as 89.7%, effectively inhibiting the structural degradation caused by FT cycles and high moisture levels. 4. The two-dimensional slope model constructed using COMSOL Multiphysics shows that, at a lower moisture content (7.6%), the maximum plastic strain at the critical instability of the slope is approximately 0.20. At moisture contents of 9.6% and 11.6%, instability occurs earlier at 106 and 15 FT cycles, respectively, with the maximum plastic strain increasing to 1.515 and 2.465, indicating that the moisture content has a decisive impact on slope stability. While the experimental-numerical framework developed here offers valuable insights, several limitations remain:The laboratory specimens (\(\varphi\) = 101 mm, h = 210 mm) do not reflect the full heterogeneity of natural slopes, including macro-cracks, layering, or scale-dependent behavior. The FT cycles were performed under idealized and accelerated conditions (\(\pm\)20 \({}^{\circ}\)C, 12 h intervals), which may not mimic gradual seasonal transitions. No external water was supplied during cycles, potentially underestimating the effects of rainwater infiltration or snowmelt recharge. The numerical slope model assumes homogeneity and isotropy without considering stratification, moisture migration, or chemical weakening. Strength degradation was modeled using exponential fits, which lack mechanistic thresholds or time-dependent acceleration. Future work will explore coupled thermal-hydraulic-mechanical-chemical (THMC) models, meso-scale physical tests, and large-scale field validation to enhance predictive capacity under real climate conditions. These findings are particularly applicable to seasonally frozen, coarse-grained soils in regions such as southeastern Qinghai-Xizang, Alaska, and Scandinavia. However, caution is advised in extrapolating the results to fine-grained soils or highly stratified, anisotropic slope systems. Future studies integrating multi-field coupling, moisture redistribution, and time-dependent chemical degradation will be crucial to improving the universality and robustness of the proposed framework. H.N. : Conceptualization, Data curation, Methodology, Validation, Writing--original draft. P.W. : Conceptualization, Funding acquisition, Supervision, Writing--review and editing. L.C. : Conceptualization, Formal Analysis, Funding acquisition. W.Z. : Conceptualization, Methodology, Supervision, Validation, Writing--review and editing. D.S. : Conceptualization, Data curation, Writing--review and editing. C.S.