The entrance of permafrost tunnels in cold regions is particularly vulnerable to frost damage caused by complex thermal-hydro-mechanical (THM) interactions in unsaturated frozen soils. The effects of temperaturedependent volumetric strain variations across different stratum materials on heat and moisture transport are often neglected in existing THM coupling models. In this study, a novel THM coupled model for unsaturated frozen soil integrating volumetric strain correction is proposed, which addresses bidirectional interactions between thermal-hydraulic processes and mechanical responses. The model was validated through laboratory experiments and subsequently applied to the analysis of the Yuximolegai Tunnel. The results indicate that distinct layered ice-water distribution patterns are formed in shallow permafrost under freeze-thaw cycles, driven by bidirectional freezing and water migration. Critical mechanical responses were observed, including a shift in maximum principal stress from the invert (1.40 MPa, frozen state) to the crown (5.76 MPa, thawed state), and periodic lining displacements (crown > invert > sidewalls). Frost damage risks are further quantified by the spatial-temporal zoning of ice-water content-sensitive regions. These findings advance unsaturated frozen soil modeling and provide theoretical guidance for frost-resistant tunnel design in cold regions.

The complex multiphase composition of frozen soil induces significant coupling interactions between the thermal, hydrological, mechanical, and damage fields during deformation, particularly under dynamic loading conditions. This study presents a hybrid decomposition phase-field model to investigate the multi-field coupling behavior and damage mechanisms of frozen soil. Unlike the spectral decomposition model, the proposed framework integrates isotropic degradation and the spectral decomposition methods, thereby enabling the simulation of damage evolution under compressive-dominated loading conditions. The model incorporates the viscous effects and strain rate sensitivity to accurately capture the dynamic response of frozen soil and establishes governing equations for coupled displacement, temperature, and fluid pressure fields. The applicability of the model was validated through confined compression experiments on frozen soil, demonstrating its capability to predict distinctive damage features, such as compaction bands oriented perpendicular to the loading direction, which represent the competitive interaction between the softening mechanism of pore collapse and the hardening mechanism of microstructural densification. This study provides significant advancements in the theoretical understanding and numerical simulation of the dynamic mechanical behavior of frozen soil.

The combination of vacuum electro-osmosis treatment and electrokinetic remediation allows for the simultaneous consolidation and remediation of contaminated sediments, involving multiple coupled fields such as electrical field, hydraulic field, mechanical field, and chemical field. This study couples the charge conservation, vacuum electro-osmosis consolidation, and contaminant transport equations under vacuum electro-osmosis conditions to establish a numerical model for the consolidation and remediation process. Laboratory experiments were conducted for comparative analyses. The numerical results show that the electric field intensity decays from both sides towards the center. However, the other positions align well with the experimental results, indicating the ability of the numerical model to reflect the non-uniform distribution of soil potential. The anode and cathode regions become negative pressure centers, resulting in an increasing seepage velocity towards the negative pressure centers. The numerical results accurately capture the trend of pore water pressure development before 40 h, although the absolute value obtained after 40 his slightly overestimated. Additionally, the numerical results demonstrate a 47% removal efficiency of copper at the anode after 48 h, which is consistent with the experimental results. The distribution of electric field and contaminants are affected by the shape of the electrode board.

Permafrost regions of Qilian Mountains in China are rich in gas hydrate resources. Once greenhouse gases in deep frozen layer are released into the atmosphere during hydrate mining, a series of negative consequences occur. This study aims to evaluate the impact of hydrate thermal exploitation on regional permafrost and carbon budgets based on a multi-physical field coupling simulation. The results indicate that the permeability of the frozen soil is anisotropic, and the low permeability frozen layer can seal the methane gas in the natural state. Heat injection mining of hydrates causes the continuous melting of permafrost and the escape of methane gas, which transforms the regional permafrost from a carbon sink to a carbon source. A higher injection temperature concentrates the heat and causes uneven melting of the upper frozen layer, which provides a dominant channel for methane gas and results in increased methane emissions. However, dense heat injection wells cause more uniform melting of the lower permafrost layer, and the melting zone does not extend to the upper low permeability formation, which cannot provide advantageous channels for methane gas. Therefore, a reasonable and dense number of heat injection wells can reduce the risk of greenhouse gas emissions during hydrate exploitation.

Due to rainfall, the soil-rock differential weathering interface of spherical weathered granite soil slopes is prone to evolve into a dominant seepage channel and undergo seepage suffosion, which accelerates the deformation and instability of these slopes. However, little research has been carried out on the characteristics of seepage suffosion and the migration of fine particles. Based on the unsaturated seepage theory of porous media, a numerical calculation framework is established to accurately describe the seepage suffosion process at the soil-rock interface, considering the coupling relationship between the fine particle migration, suffosion initiation response and unsaturated seepage. The finite element method is used to construct a seepage suffosion model for unsaturated granite residual soil under the effect of dominant flow. Based on the seepage suffosion process of homogeneous soil columns, the suffosion characteristics of dominant flow under three typical soil-rock interface burial states are systematically investigated. The results show that the soil-rock interface and the matrix permeability of spherical weathered granite soil slopes are highly variable, with the wetting front forming a downward depression infiltration funnel, and the degree of depression of the wetting front becomes more pronounced as rainfall continues. The degree of fine particle loss is related to the burial state of the soil-rock interface, in which the dominant flow potential suffosion of the under-filled soil condition is the most significant, and even excess pore water pressure occurs at the interface, which is the most unfavorable to the stability of this type of slope. The research results can provide a scientific basis for accurately evaluating the stability of spherical weathered granite soil slopes under rainfall conditions.