## 5 Conclusions  
This study primarily investigates the shear mechanical properties and microscopic pore characteristics of Hipparion laterite--the primary slip zone stratum controlling the initiation and evolution of loess landslides in the Northern Shaanxi region. Using a combination of indoor ring-shear tests and SEM analyses, the shear damage patterns and shear stress-mean linear displacement curves of Hipparion laterite specimens subjected to 0-10 F-T cycles under varying initial moisture contents were examined. Both qualitative and quantitative analyses of the pore microstructure were performed to understand the strength deterioration mechanism. The key findings are summarized below:  
(1) The F-T-induced deformation patterns of Hipparion laterite manifest progressive structural degradation. During initial cycles, pore spaces and microfractures proliferate, followed by the development and coalescence of serrated and transverse cracks with subsequent cycles. Under prolonged cycling, interconnected diagonal fissures propagate across specimens alongside frost-induced crystalline networks, demonstrating persistent structural damage. Variations in moisture content and cycle intensity exacerbated this degradation, culminating in a total mass loss of 0.94%--notably lower than that observed in typical loess deposits. (2) The shear stress-mean linear displacement curves of Hipparion laterite specimens revealed three characteristic stages: strain development (Stage I), strain-softening (Stage II), and sustained strain-hardening (Stage III). Specimens with 16% and 20% moisture content transitioned from Stage I to Stage II, while those with 24% moisture content entered Stage III after six F-T cycles. The peak and residual strengths decreased by 46.27-96.93 kPa and 48.72-70.66 kPa, respectively. Cohesion followed an exponential decay relationship with the F-T cycles, whereas the internal friction angle exhibited an exponential increase. (3) F-T cycling weakens interparticle cementation, progressively transforming mineral contact modes from strongly bonded face-to-face interactions to weaker edge-to-edge and point-to-point configurations. Micropore proportion decreased to 23.57-28.62%, transitioning to dominance by small and mesopores, which increased the apparent porosity to a maximum of 0.3967. At 24% initial moisture content, pore orientation alignment diminished, while elevated probabilistic entropy (\(\Delta\)H = 0.0401) and the fractal dimension (\(\Delta\)D = 0.0589) indicated heightened structural disorder and complexity. Among factors influencing pore microstructure, moisture content emerged as the dominant controlling parameter. (4) The internal architecture of the soil and the form of elements during the F-T stages (freezing, warming, and thawing) contributed to significant reductions in mechanical  
Figure 18: Microscopic mechanism of water migration in Hipparion laterite during F-T process. (**a–d**) represent the initial freezing stage, sustained freezing stage, post-freezing warming stage, and sustained thawing stage of the soil, respectively. strength. This result was attributed to variations in internal and external temperatures, intergranular voids, and agglomerate sizes. Conceptualization, T.P. and Z.Z. ; methodology, T.P. and Z.Z. ; software, T.P. ; validation, J.M. and F.L. ; formal analysis, T.P. ; investigation, Z.Z., T.P., J.M. and F.L. ; data curation, T.P. ; writing--original draft preparation, T.P. and Z.Z. ; writing--review and editing, Z.Z. ; visualization, T.P. ; supervision, J.M. and F.L. ; All authors have read and agreed to the published version of the manuscript. This research was funded by the National Natural Science Foundation of China (41302276) and the Scientific Research Project of Geological Research Institute for Coal Green Mining, Xi'an University of Science and Technology (MTy2019-22). Not applicable. The original contributions presented in the study are included in the article; further inquiries can be directed to the corresponding author.