This study investigates the freezing process and mechanical impact behavior of saturated soil to provide new insights into soil thermodynamic and improve its comprehensive investigation under a cryogenic engineering environment. The unfrozen water content is a major focus of study during soil freezing. Many studies have proposed models for calculating the unfrozen water content in frozen and unfrozen pores. However, they lack uniformity and consistency on a physical basis and mathematical derivation. An unified theoretical model was derived based on the principle of thermodynamic equilibrium. The main theoretical results indicated that the dimensionless total volume of the unfrozen water membrane in the frozen pores first increased and then decreased with increasing temperature, revealing the temperature effect on the unfrozen water content in frozen pores. By combining the theoretical model with the distinct element method (DEM), water freezing into ice in saturated soil was numerically simulated using two modes of particle expansion. One of the two modes proposed by the authors was to change the coefficient of expansion during saturated soil freezing to further consider the non-linear variation in unfrozen water content. Subsequently, the effects of the two modes on crack generation during saturated soil freezing were compared and analyzed. Finally, based on the dissipation energy produced in particle contacts, a method for calculating the rises in impact temperature in different particles was proposed for revealing the local and discrete changes in frozen saturated soil under impact loading. The main numerical results indicated that the proportion of the number of particles for different temperature rise ranges followed a Weibull distribution, and the average temperature rise of the particles near the incident end was higher than that of the particles near the transmission end.

The pile-anchor structure is widely used in slope/landslide reinforcement, and is also applicable to debris flow and rockfall barriers in mountainous areas. However, the impact behavior of this structure has not been studied. To promote the use of this retaining structure in the prevention of slope geological disasters, this study investigated the dynamic responses and impact behavior of pile-anchor structures through a set of impact experiments, wherein dry granular materials with different particle size and sliding blocks with different masses were adopted to simulate different impact loading scenarios of granular flow and rockfall. The impact pressure on the pile-anchor structure, the seismic signals induced inside the slope during the sliding and impact processes, and the deformation characteristics and failure modes of the piles and anchors were systematically investigated. The results indicate that the peak impact force and intensity of the seismic signal are affected by the particle size of the impact granular materials. As the impact loading of sliding blocks increased, the tensile force of the anchor increased nonlinearly, the distribution pattern of the pile's impact dynamic moment changed, and anchor prestress loss was observed. The preliminary results obtained by this study are expected to provide the theoretical basis for designing relevant barriers in areas prone to debris flow and rockfall, and promote the inclusivity of the impact behavior of slope retaining structures in existing design codes pertaining to retaining structures.