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.

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.

Physics-informed neural networks (PINNs) are increasingly employed for surrogate modelling of soil behaviour. Existing surrogate models for unsaturated soil only account for seepage in rigid soil, neglecting the complex coupling between deformation and seepage in unsaturated soil. This study develops a new surrogate model for hydro-mechanical coupling in unsaturated soil using the PINN approach. Dimensionless governing equations, including mass balance and force balance equations, are derived and adopted for physical constraints. With absence of explicit constitutive relations, this new surrogate model utilises sparse measured data to identify pore water pressure, effective stress and deformation in unsaturated soil. Separate neural networks are employed to facilitate efficient back-propagation for coupled problem involving multiple outputs. The newly developed model is then applied to simulate two cases with sparse measurements in unsaturated soil. The results illustrate that the newly developed surrogate model successfully learns the elasto-plastic constitutive relation of suction-induced volume change from experimental data. Meanwhile, model predictions regarding both water flow and stress distribution align within the 95 % confidence interval of theoretical values, demonstrating interpretability of PINN model. Furthermore, by adhering to physical constraints, the relative error in predicting soil deformation from neural networks significantly reduces from 49 % to less than 10 %. These findings suggest PINN model with separate networks is capable to simulate unsaturated soil considering both deformation and seepage, even with sparse measured data and incomplete physical constraints.

This study investigates the influence of primary variables selection on modeling non-isothermal two-phase flow, using numerical simulation based on the full-scale engineered barrier system (EBS) experiment conducted at the Horonobe Underground Research Laboratory (URL) as part of the DECOVALEX-2023 project. A thermalhydraulic coupled model was validated against analytical solution and experimental data before being applied to simulate the heterogeneous porous media within the EBS. Two different primary variable schemes were compared for discretizing the governing equations, revealing substantial differences in results. Notably, using capillary pressure as a primary variable instead of saturation resulted in closer alignment with analytical solutions and real-world observations. While the modeling work at the Horonobe URL generally exhibited trends consistent with experimental data, discrepancies were attributed to the operational conditions of the heater and the influence of the Excavation Damaged Zone (EDZ) near the borehole.

The evaluation of thermo-hydro-mechanical (THM) coupling response of clayey soils has emerged as an imperative research focus within thermal-related geotechnical engineering. Clays will exhibit nonlinear physical and mechanical behavior when subjected to variations in effective stress and temperature. Additionally, temperature gradient within soils can induce additional pore water migration, thereby resulting in a significant thermo-osmosis effect. Indeed, thermal consolidation of clayey soils constitutes a complicated THM coupling issue, whereas the theoretical investigation into it currently remains insufficiently developed. In this context, a one-dimensional mathematical model for the nonlinear thermal consolidation of saturated clay is proposed, which comprehensively incorporates the crucial THM coupling characteristics under the combined effects of heating and mechanical loading. In current model, the interaction between nonlinear consolidation and heat transfer process is captured. Heat transfer within saturated clay is investigated by accounting for the conduction, advection, and thermomechanical dispersion. The resulting governing equations and numerical solutions are derived through assuming impeded drainage boundaries. Then, the reasonability of current model is validated by degradation and simulation analysis. Subsequently, an in-depth assessment is carried out to investigate the influence of crucial parameters on the nonlinear consolidation behavior. The results indicate that increasing the temperature can significantly promote the consolidation process of saturated clay, the dissipation rate of excess pore water pressure (EPWP) is accelerated by a maximum of approximately 15%. Moreover, the dissipation rate of EPWP also increases with the increment of pre-consolidation pressure, while the corresponding settlement decreases. Finally, the consolidation performance is remarkably impacted by thermo-osmosis and neglecting this process will generate a substantial departure from engineering practice.

This paper examines the thermo-hydro-mechanical (THM) coupling behavior of layered transversely isotropic media under axisymmetric and plane strain conditions by utilizing the transformed differential quadrature method (TDQM), taking groundwater into consideration. Initially, the coupled governing equations of layered transversely isotropic media in multi-dimensional coordinate systems are established with considering the influence of groundwater levels. Subsequently, appropriate integral transform methods are applied to derive ordinary differential equations under different coordinate systems. It can be seen that the equations in different coordinate systems after the discretization are similar. Boundary conditions and internal continuity conditions are defined through the stress-strain relationship in the transformed domains, which are integrated into the discretized equations to form the global matrix equations. After solving the matrix equations, this study verifies the solution and investigates the impact of groundwater levels and the key parameters of transverse isotropy, and compares the behaviors of the media in different coordinate systems.

The artificial freezing method is commonly used in tunneling beneath overlying structures due to the significant development and utilization of underground space. However, there is a growing demand for controlling frost heave deformation in overlying structures and the interaction laws of these structures during freezing and undercutting remain unclear. Hence, a multi-physics coupling deformation calculation method is proposed. This study focuses on the shield tunneling project of Shanghai Metro Line 18 at Guoquan Road Station, which intersects with the existing upper operating station of Line 10. It investigates the construction approach for new tunnels during freezing, using the gray clay of layer ? 1 in Shanghai as the research target, particularly examining the disruptive effects on the primary structures of the upper operating station. Considering water migration, we derived the frost heave deformation formula and developed an improved thermo-hydro-mechanical coupling theory model by using pore ratio, freezing temperature, and average water pressure as coupling variables. Through frost heave tests on cohesive soil, we obtained the stress-strain relationship of frost heave specimens to describe the changes in pore structure. Subsequently, a thermo-hydro-mechanical three-field coupling numerical calculation was conducted using the weak form module (PDE) of COMSOL Multiphysics software. The simulation results closely matched the monitoring data and were below the predetermined control value, validating the accuracy of the enhanced coupling theory. These findings offer a multi-physics coupling approach for calculating deformations in similar frozen underpass tunnels, serving as a valuable reference for freezing method design and construction parameters. Additionally, we propose safety control indicators for reinforcement construction based on this scientific groundwork.

This paper presents a comprehensive computational model for analyzing thermo-hydro-mechanical coupled processes in unsaturated porous media under frost actions. The model employs the finite element method to simulate multiphase fluid flows, heat transfer, phase change, and deformation behaviors. A new soil freezing characteristic curve model is proposed to consider the suctions from air-water capillary pressure and water-ice cryosuction. A total pore pressure with components from liquid water pressure, air pressure, and ice pressure is used in the effective stress law. Vapor and dry air are considered miscible gases, utilizing the ideal gas law and Dalton's law. The governing equations encompass the linear momentum balance equation, the energy balance equation, and mass conservation equations for water species (ice, liquid, and vapor) and dry air. Weak forms are formulated based on primary variables of displacement, water pressure, air pressure, and temperature. The spatial discretization is achieved through the finite element method, while temporal discretization employs the fully implicit finite difference method, resulting in a system of fully coupled nonlinear equations. To verify the proposed computational model, a numerical implementation is developed and validated against a set of experimental data from the literature. The successful verification demonstrates the robustness of the model. A detailed discussion of the contributions from phase change strain and different sources of pore pressure is also addressed.

This study constructs a multilayered transversely isotropic saturated model under thermal and horizontally circular loads, and further investigates the model's thermo-hydro-mechanical coupling response. Firstly, the ordinary differential matrix equations of thermoelastic saturated media in the integral transformed domain are derived. Secondly, the solution for multilayered thermoelastic saturated media is developed using the extended precise integration method (EPIM), along with the boundary conditions at both ends of the foundation and the continuity conditions between adjacent layers. After that, the solution in the physical domain is further attained with the use of Laplace-Hankel integral transform inversion. Finally, the accuracy of the proposed theory is confirmed through numerical examples, and the influences of anisotropic parameters, the soil's stratification and porosity on the thermo-hydro-mechanical coupling response of the media are studied.

Rainfall-induced landslides are common natural hazards, particularly in cases involving unsaturated soils. Slope instability issues may arise due to extreme climate events, while, creep effects can also contribute to landslide problems. In this study, a modified ViscoElastic-ViscoPlastic constitutive model is developed to more accurately characterise the mechanical properties of unsaturated loess, considering stress-level dependency of stiffness and creep properties. In addition, to better characterise the collapsibility of loess, the relationship between strengths and matric suction has been introduced. The infiltration process of an unsaturated porous medium is illustrated by the Van Genuchten model and the generalized Darcy ' s law. Additionally, the atmospheric boundary condition is incorporated in the numerical simulations, considering factors such as runoff generation and various climate events. In the context of slope stability analysis, a numerical approach has been developed to determine the safety factor of the slopes, by using displacement changes as the key assessment criterion. A good agreement between numerical and analytical results has been observed, verifying the proposed approach to determining safety factor. Finally, in parametric analyses, the effects of creep and matric suction on safety factor have been identified. Slope stability of unsaturated loess slopes subjected to different rainfall intensities and rainfall durations has been studied. The maximum depth of the sliding part increases obviously when considering the contribution of creep deformations, which is crucial in analysing slope stability.