In order to investigate the frost-heaving characteristics of wintering foundation pits in the seasonal frozen ground area, an outdoor in-situ test of wintering foundation pits was carried out to study the changing rules of horizontal frost heave forces, vertical frost heave forces, vertical displacement, and horizontal displacement of the tops of the supporting piles under the effect of groundwater and natural winterization. Based on the monitoring condition data of the in-situ test and the data, a coupled numerical model integrating hydrothermal and mechanical interactions of the foundation pit, considering the groundwater level and phase change, was established and verified by numerical simulation. The research results show that in the silty clay-sandy soil strata with water replenishment conditions and the all-silty clay strata without water replenishment conditions, the horizontal frost heave force presents a distribution feature of being larger in the middle and smaller on both sides in the early stage of overwintering. With the extension of freezing time, the horizontal frost heave force distribution of silty clay-sand strata gradually changes from the initial form to the Z shape, while the all-silty clay strata maintain the original distribution characteristics unchanged. Meanwhile, the peak point of the horizontal frost heave force in the all-silty clay stratum will gradually shift downward during the overwintering process. This phenomenon corresponds to the stage when the horizontal displacement of the pile top enters a stable and fluctuating phase. Based on the monitoring conditions of the in-situ test, a numerical model of the hydro-thermo-mechanical coupling in the overwintering foundation pit was established, considering the effects of the groundwater level and ice-water phase change. The accuracy and reliability of the model were verified by comparison with the monitoring data of the in-situ test using FLAC3D finite element analysis software. The evolution of the horizontal frost heaving force of the overwintering foundation pit and the change rule of its distribution pattern under different groundwater level conditions are revealed. This research can provide a reference for the prevention of frost heave damage and safety design of foundation pit engineering in seasonal frozen soil areas.

Accurately modeling soil-fluid coupling under large deformations is critical for understanding and predicting phenomena such as slope failures, embankment collapses, and other geotechnical hazards. This topic has been studied for decades and remains challenging due to the nonlinear responses of geotechnical structures, which typically result from plastic yielding and finite deformation of the soil skeleton. In this work, we comprehensively summarize the theory involved in the soil-fluid coupling problem. Within a finite strain framework, we employ an elasto-plastic constitutive model with linear hardening to represent the solid skeleton and a nearly incompressible model for water. The water content influences the behavior of the solid skeleton by affecting its cohesion. The governing equations are discretized by material point method and two sets of material points are employed to independently represent solid skeleton and fluid, respectively. The proposed method is validated by comparing simulation results with experimental results for the impact of water on dry soil and wet soil. The capability of the method is further demonstrated through two cases: (1) the impact of a rigid body on saturated soil, causing water seepage, and (2) the filling of a ditch, which considers the erosion of the foundation. This work may provide a versatile tool for analyzing the dynamic responses of fluid and solid interactions, considering both mixing and separation phenomena.

In urban subway construction, shield tunneling near pile groups is common, where additional loads may threaten existing structures. This study establishes multiple 3D nonlinear FDM models with fluid-solid coupling to investigate how tunnel-pile clearances (Hc) affect the mechanical response of low-cap pile groups (2 x2) during side-by-side twin tunneling in composite strata. The advanced CYSoil model, incorporating nonlinearity, strain path dependency, and small strain behavior, is employed to simulate soil response. Results show that tunneling induces up to a similar to 66.7 % reduction in pore water pressure, forming a funnel-shaped seepage pattern. As Hc increases from 0.8D to 2.6D, the low-pressure zone shifts from sidewalls to vault and invert, while maximum displacements reduce by up to 14.04 mm (lateral), 5.28 mm (transverse), and 19.68 mm (vertical). Axial force evolution in piles follows a three-stage decline, i.e., rapid, slow, and moderate, with peak shaft resistance concentrated near the tunnel axis. These findings aid in optimizing tunnel-pile configurations and mitigating geotechnical risks.

A novel thermo-hydro-mechanical-chemical (THMC) coupling model grounded in thermodynamic dissipation theory was established to unravel the intricate behavior of unsaturated sulfate-saline soils during cooling crystallization. The model quantifies energy transfer and dissipation during crystallization and introduces a method to calculate the amount of sulfate crystallization. It intricately captures the interdependencies between crystallization, pore water pressure, crystallization pressure and volumetric expansion, while also accounting for the dynamic feedback of latent heat from phase transitions on heat conduction. The reliability of the model was validated through experimental data. Numerical simulations explored the effects of cooling paths, thermal conductivity, initial salt content and initial porosity on the crystallization behavior and mechanical properties. The model provides theoretical support for optimizing the engineering design and facility maintenance of sulfatesaline soils.

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.

Three-dimensional numerical models are developed to investigate the anti-liquefaction of ordinary (OSCs) and geosynthetic-encased (GESCs) stone columns in sandy soil under sinusoidal loading using the fluid-solid coupling method. The validated models capture and compare the vertical and radial deformation, excess pore water pressure (EPWP), and vertical effective stress of OSC, GESC, and sandy soil. Furthermore, ten essential factors are selected to conduct the parametric study. Numerical results reveal that GESC is more suitable for improving sandy soil and resisting dynamic load considering the deformation and EPWP. The bulging deformation is no longer the primary reason for failure. The partial encasement (e.g., 1-2D, D = column diameter) and short floating and end-bearing GESCs (e.g., 1-2.5D) are not recommended for reinforcing the sandy soil. GESC is more sensitive to low-frequency and high-amplitude loads, with shear and bending, whereas displays a block movement under higher frequency and lower amplitude loading. The change in loading amplitude is more disadvantageous to GESC than loading frequency. GESC with a large diameter cannot effectively resist the dynamic loads.

For many solids, irreversible deformation is often accompanied by changes in the internal structure, impacting the reversible responses, a phenomenon termed elasto-plastic coupling. This coupling has been observed experimentally in various geomaterials, including clayey and sandy soils, as well as hard and soft rocks. Fabric anisotropy, which characterizes the internal structure, is a distinct feature of soils and significantly influences both reversible and irreversible behaviors. In this study, we adopted a coupling formulation based on the framework of anisotropic critical state theory (ACST) to describe the anisotropic elasto-plastic coupling response of soils. The formulation incorporates a deviatoric fabric tensor F, which consistently quantifies the internal structure of soils in both reversible and irreversible range, into a hyperelastic formulation and a plastic model, respectively. A novel evolution rule of F, defined based on the current stress ratio and plastic strain, is proposed, where the direction gradually aligns with the loading direction and the norm achieves different asymptotic values depending on the applied loading paths. This allows for the representation of evolved anisotropy effects on elasticity, dilatancy and strength simultaneously, providing a natural description of elasto-plastic coupling. Within this coupling framework, any anisotropic model within ACST can serve as the plastic platform for developing the elasto-plastic coupling models with anisotropic hyperelasticity. Herein, a bounding surface plastic model is utilized for illustration. The proposed model's performance is demonstrated by especially comparing simulated results to test data on evolving elastic stiffness ratios and overall elastoplastic responses under varying monotonic and cyclic loading conditions.

This study investigates a unique type of soil, turfy soil, which is characterized by poor engineering geological properties and high organic matter content, widely distributed in the seasonally frost regions of Northeast China. The research discusses its freezing-thawing characteristics and the thermo-hydro-mechanical properties during the freezing-thawing process, which is of significance implications for parameter selection and frost heave settlement considerations in engineering construction within cold regions with high-organic-matter soil distribution. Unidirectional frost heave-thaw tests were conducted in the laboratory. Accurate hydrothermal characteristic parameters during freezing and thawing of a turfy soil were obtained by NMR and steady-state comparison method. Based on Fourier's law, the Richard equation, and considering latent heat of phase change and volume change during ice-water phase transition, a turfy soil-water-thermal-mechanical coupling model was proposed. Validation of this model using COMSOL Multiphysics showed that the errors between the frost heave and thaw subsidence of each soil layer and the measured values from tests were in the range of 1.75-3.6 mm and 0.75-1.73 mm, indicating a good fit. According to the simulation value, the turfy soil can be designated as strong freezing and thawing soil, matching reality. The results of this study provide a theoretical basis for the construction of roadbed and foundation project in the seasonally frozen turfy soil distribution areas and serve as a basis for frost damage prevention and control.

When analyzing the dynamics of wind turbines under the action of wind and ground motion, mass-point models cannot accurately predict the dynamic response of the structure. Additionally, the coupling effect between the pile foundation and the soil affects the vibration characteristics of the wind turbine. In this paper, the dynamic response of a DTU 10 MW wind turbine under the coupling effect of wind and an earthquake is numerically studied through the combined simulation of finite-element software ABAQUS 6.14-4 and OpenFAST v3.0.0. A multi-pile foundation is used as the foundation of the wind turbine structure, and the interaction between the soil and the structure is simulated by using p-y curves in the numerical model. Considering the coupling effect between the blade and the tower as well as the soil-structure coupling effect, this paper systematically investigates the vibration response of the blade-tower coupled structure under dynamic loads. The study shows that: (1) the blade vibration has a significant impact on the tower's vibration characteristics; (2) the ground motion has varying effects on blades in different positions and will increase the out-of-plane vibration of the blades; (3) the SSI effect has a substantial impact on the out-of-plane vibration of the blade, which may cause the blade to collide with the tower, thus resulting in the failure and damage of the wind turbine structure.

Coupled nonlinear thermo-hydro-mechanical finite element simulations were carried out to investigate the behavior of energy micropiles subjected to thermal loading cycles. Two kinds of problems were analyzed: The case of an isolated micropile, for which comparison with previous research on medium-size isolated energy pile is provided, and the case of large groups of micropiles, with the aim of investigating the interaction effects. In both problems, micropiles were considered installed in a thick layer of very soft, saturated clay, characterized by isotropic or anisotropic hydraulic conductivity. Two advanced existing hypoplastic models, one incorporating the thermal softening feature, were used to describe the clay behavior in both problems. The settlements of the micropile head were found to increase during thermal cycles under constant mechanical load, showing a sort of ratcheting. For micropile groups, the settlement increase rate was faster as the spacing between micropiles was reduced. The excess pore water pressures developed at the micropile-soil interface played a significant role on the deformation and displacement fields of the soil-micropile systems, especially in the case of micropile groups, affecting the shear strength developed at the micropile-soil interface. The consolidation process was faster when the hydraulic conductivity was anisotropic, meaning that the development of excess pore water pressure was reduced in this case. As the spacing between the micropiles increased, i.e., as thermal interaction decreased, the heat flux exchanged by a micropile of the group during one cycle approached the heat flux exchanged by an isolated micropile in the same period.