Energy piles, which serve the dual functions of load-bearing and geothermal energy exchange, are often modeled with surrounding soil assumed to be either fully saturated or completely dry in existing design and computational methods. These simplifications neglect soil saturation variability, leading to reduced predictive accuracy of the thermomechanical response of energy piles. This study proposes a novel theoretical framework for predicting the thermo-hydro-mechanical (THM) behavior of energy piles in partially saturated soils. The framework incorporates the effects of temperature and hydraulic conditions on the mechanical properties of partially saturated soils and pile-soil interface. A modified cyclic generalized nonlinear softening model and a cyclic hyperbolic model were developed to describe the interface shear stress-displacement relationship at the pile shaft and base, respectively. Governing equations for the load-settlement behavior of energy piles in partially saturated soils were derived using the load transfer method (LTM) and solved numerically using the matrix displacement method. The proposed approach was validated against experimental data from both field and centrifuge tests, demonstrating strong predictive performance. Specifically, the average relative error (ARE) was less than 15% for saturated soils and below 23% for unsaturated soils when evaporation effects were considered. Finally, parametric analyses were conducted to assess the effects of flow rate, groundwater table position, and softening parameters on the THM behavior of energy piles. This framework can offer a valuable tool for predicting THM behavior of energy piles in partially saturated soils, supporting their broader application as a sustainable foundation solution in geotechnical engineering.

The coupled thermo-hydro-mechanical response caused by fire temperature transfer to surrounding rock/soil has a significant impact on tunnel safety. This study developed a numerical simulation model to evaluate the effects of fire on tunnel structures across different geological conditions. The heat transfer behavior varied with the mechanical properties and permeability of the geotechnics, concentrating within 1.0 m outside the tunnel lining and lasted for 10 days. Significant differences in pore water pressure changes were observed, with less permeable geologies experiencing greater pressure increases. Tunnel deformation was more pronounced in weaker geotechnics, though some tunnels in stronger geologies showed partial recovery post-fire. During the fire, thermal expansion created a bending moment, while a negative bending moment occurred after the fire due to tunnel damage and geotechnical coupling. The entire process led to irreversible changes in the bending moment. The depth of tunnel burial showed varying sensitivity to fire across different geological settings. This study provides important references for fire protection design and post-fire rehabilitation of tunnels under diverse geological conditions.

This paper presents coupled thermo-hydro-mechanical finite element analyses (FEAs) of undrained uplift capacity for buried offshore pipelines operating at elevated temperature. An anisotropic thermoplastic soil constitutive model was employed to simulate mechanical behaviour of seabed soil under the combined actions of thermal and mechanical loading. FEAs investigated the influences of different parameters, e.g., pipeline embedment depth, pipe-soil interface roughness, duration of pipeline operation, and operating temperature, on pipeline uplift capacity. Time-dependent evolutions of temperature and excess pore water pressure were also tracked in soil surrounding the pipeline. For different durations of pipeline operation, FEA results revealed an improvement in normalized uplift capacity Nu of pipelines operating under elevated temperature. However, such an increase in Nu was diminished by a maximum of 7 % with increase in the ratio RTH of thermal diffusivity to coefficient of consolidation of surrounding soil. For different normalized pipeline embedment, 20-30 % enhancement of Nu was observed after six months of pipeline operation at 60 degrees C. However, after six months of operation, further improvement in Nu was negligible. Based on FEA results, this paper proposes an equation to estimate pipeline uplift capacity as a function of operating temperature, depth of embedment, and duration of pipeline operation.

To better characterize the intricate coupled thermo-hydro-mechanical dynamic (THMD) response in twodimensional saturated soil and to enrich the research object of Green-Naghdi (G-N) generalized thermoelastic theory, this study innovatively combines the G-N generalized thermoelastic theory and Caputo's fractional order derivative, to obtain the new control equations, and to establish a new fractional order thermoelastic theoretical model. The article is solved by the normal mode analysis (NMA), which can eliminate the integration error and solve the complex fractional order partial differential control equations quickly at the same time. The effects of different boundary conditions of fractional order derivatives, porosity, frequency, and thermal conductivity coefficients on non-dimensional excess pore water pressure, temperature, vertical displacement, and vertical stress are also fully analyzed, and the distribution curves of high precision numerical solutions are given. The results show that the effect of frequency variation on each non-dimensional variable is obvious. The effects of fractional order derivatives, porosity and thermal conductivity coefficients on the non-dimensional variables vary depending on the boundary conditions. The results provide theoretical support for geotechnical and environmental engineering.

This paper introduces a thermo-hydro-mechanical (THM) framework to model thaw consolidation in permafrost regions. By integrating internal energy degradation functions and a modified Cam-Clay model within a phase-field damage framework, the model focuses on simulating the simultaneous effects of phase change and particle rearrangement. The model integrates two distinct phase-field variables with the modified Cam-Clay plasticity framework. One phase-field variable monitors pore phase composition, while the other captures particle rearrangement. These variables are directly coupled to the constitutive model, providing critical data for updating the stress-strain relationship by accounting for particle rearrangement-induced softening and hardening effects due to volumetric deformation. The model converges to the modified Cam-Clay model when there is no phase change. This approach addresses a significant gap in existing models by capturing the associated microstructural evolution and plastic softening in thaw-sensitive soils. Validation efforts focus on experimental scenarios assessing both the mechanical impacts of thaw consolidation and the dynamics of phase transitions, particularly emphasizing latent heat effects. The results demonstrate the proposing model's capability of handling complex behaviors of permafrost under thaw conditions, confirming its potential for enhancing infrastructure resilience in cold regions.

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.

This study proposes a three-dimensional transformed differential quadrature solution for the thermo-mechanical (TM) and thermo-hydro-mechanical (THM) coupling of transversely isotropic soils considering groundwater. Initially, the governing equations for TH coupling above the water table and THM coupling below the water table are introduced. Subsequently, twodimensional Fourier integral transform and Laplace integral transform are applied, and a series of equations are discretized along the depth according to the discrete rules of the transformed differential quadrature method. Then, the boundary conditions for stress, displacement, and temperature are introduced through integral transforms and stress-strain relationships. By solving the matrix equation, the solution for transversely isotropic soils is obtained. After verifying the theory in this study, continuity conditions, the water table depth, anisotropy of thermal diffusion coefficients, and seepage are analyzed, contributing to the design of radioactive waste disposal sites, energy piles, and other projects.

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 mechanical behavior of Methane Hydrate-Bearing Sediment (MHBS) is essential for the safe exploitation of Methane Hydrate (MH). In particular, the pore size and physicochemical characteristics of MHBS significantly influence its mechanical behavior, especially in clayey grain-cementing type MHBS. This study employs the Distinct Element Method (DEM) to investigate both the macroscopic and microscopic mechanical behavior of clayey grain-cementing type MHBS, focusing on variations in pore size and physicochemical characteristics. To accomplish this, we propose a Thermo-Hydro-Mechanical-Chemical-Soil Characteristics (THMCS) DEM contact model that incorporates the effects of pore size and physicochemical characteristics on the strength and modulus of MH. This THMCS model is validated using experimental data available in the literature. Using the proposed contact model, we conducted a series of investigations to explore the mechanical behavior of MHBS under conventional loading paths, including isotropic and drained triaxial tests using the DEM. The numerical results indicate that smaller pore sizes and lower water content-key physicochemical characteristics resulting from variations in electrochemical properties and the intensity of the electric field-can lead to reduced shear strength and stiffness due to the increased breakage of aggregates and weakened cementation. Additionally, heating was found to further accelerate the process of structural damage in MHBS.