## 4 Discussion  
This study investigates the mechanical degradation of Hipparion laterite under F-T cycles and moisture variations through F-T ring-shear tests, with particular emphasis on cohesion and the internal friction angle. SEM analysis revealed that F-T actions significantly disrupt soil structure, fragmenting macro-aggregates into smaller particles and increasing  
Figure 16: Pore probability entropy and directional fractal dimension. Figure 17: Relationship between the average fractal dimension of pores and the number of F-T cycles. pore volume. The high clay content enhances unfrozen water adsorption, expanding inter-particle water film thickness and amplifying particle separation. Consequently, residual cohesion decreased by 49.61% after 10 F-T cycles--a trend consistent with intact loess at a lower moisture content (18%) [8]. At elevated moisture levels (24%), cohesion loss reached 65.23%, whereas dispersive soils achieved comparable degradation at 16.76% moisture [56], demonstrating the superior initial structural integrity and mechanical strength of Hipparion laterite. The marginal increase in the residual friction angle (\(<\)5 deg) was attributed to stress redistribution during cyclic water phase transitions, which promoted particle rearrangement and enhanced intergranular friction through optimized grain packing. These findings conclusively indicate that shear strength degradation primarily stems from cohesion loss, while moisture-induced structural weakening remains a critical contributing factor. The sensitivity of clay particles to water leads to volumetric expansion and softening. F-T cycles disrupt the soil structure, causing surface and internal deformation and deterioration, ultimately reducing the mechanical strength of Hipparion laterite [79]. Water flow under varying temperatures and stress conditions can disrupt interparticle bonds, leading to alterations in the intergranular and pore structure, which in turn affects the mechanical strength of soil. Essentially, free and bound water, distributed throughout the soil, undergoes infiltration, flow, diffusion, and migration driven by intergranular forces and water potential. This leads to changes in particle-to-particle contact and arrangement and to the dynamic evolution of intergranular pore spacing. After experiencing multiple F-T cycles, the structure and properties of Hipparion laterite soil transition from a super-consolidated state to a softer state. This change is accompanied by an increase in water absorption and a rapid decline in the mechanical strength. The single F-T cycle is divided into four stages: initial cooling, continuous freezing, post-freezing warming, and continuous thawing (Figure 18). During initial cooling, the sample remained liquid, and the surface tension gradually increased. Water from small pores migrates to larger pores, and freezing initiates. As the temperature reaches its freezing point, water in larger pores freezes preferentially because of its higher freezing point than water in smaller pores. Unfrozen water from smaller pores migrates towards the freezing front, leading to ice crystal formation and subsequent expansion. This expansion exerts pressure on the surrounding soil particles, forming agglomerates of various sizes and shapes. The freezing and expansion forces, along with the water migration force, generate microcracks on the surface of the agglomerates. Additionally, the pore space between soil particles is increased. After freezing for a certain period, rising temperatures induce a phase change from solid to liquid. A small amount of meltwater erodes the pore wall and infiltrates the secondary fissures, weakening the intergranular cementation. During the subsequent thawing stage, the agglomerates and original particles are further decomposed by the abundant meltwater, leading to an increase in the volume of small pores and a decrease in the volume of large pores. However, the damage to the soil skeleton structure caused by the F-T cycles is irreversible.