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 numerical simulations of the deformation response of unsaturated embankments subjected to rainfall infiltration using a coupled hydro-mechanical constitutive model for unsaturated soils. The constitutive model accounts for the influence of degree of saturation on the stress-strain behavior and the influence of void ratio on the water retention behavior. The constitutive model was implemented in the finite difference program FLAC, calibrated using triaxial test data, and validated using measurements of wetting-induced deformations of embankment models from centrifuge tests. The validation demonstrates that the constitutive model can capture the coupled hydro-mechanical behavior of unsaturated soils under wetting conditions. Simulations of the hydro- mechanical response of unsaturated embankments subjected to rainfall infiltration indicate that the differential settlement across the top surface of the embankment between the centerline and shoulder increases significantly during rainfall infiltration, which could result in severe damage to overlying transportation infrastructure. As the rainfall infiltration increases, shear strains accumulate and form a potential failure surface at a shallow depth of approximately 2 m from the slope surface. Insights into the hydro-mechanical response of unsaturated embankments subjected to rainfall infiltration gained will be useful for considering climate change effects in design and construction of compacted embankments.

Understanding the impact of climatic conditions on the long-term performances of soils stabilized with lime and cement is of crucial importance. Most of the available studies on durability solely rely on laboratory investigations to assess the effects of exposure to environmental-driven processes such as wetting and drying, leaching, etc. In this context, a research embankment built in 2010 with an expansive soil stabilized with 4% quicklime and a mix of 2% quicklime and 3% cement was sampled in 2021. A comprehensive experimental campaign was conducted using these samples to evaluate the performance of materials 11 years after the construction of the structure. The studies were completed by microstructural and physico-chemical investigations to understand the mechanisms that might explain changes in performance over time. The analysis of the hydro-mechanical properties of the soil sampled between the edge and the interior of the embankment was first performed. The results indicated that the material taken near the surface had a mechanical behavior equivalent to the untreated soil, demonstrating a total loss of the benefit brought by lime/cement addition. Towards the internal part of the embankment, the mechanical performance progressively increased. Physico-chemical investigations showed that on the edge of the backfill significant part of the calcium was leached 11 years after the construction. This was associated to a drop of pH, and to the formation of calcite. The microstructure was also significantly altered on the edge of the embankment compared to the internal part of the structure. Based on these results, a new mechanism of soil deterioration driven by climatic conditions was proposed. Water circulation and carbonation, associated to a significant reorganization of the microstructure were identified as the main phenomena responsible for the degradation of the treatment effects. This study showed that embankment slopes built with lime and cement stabilized expansive clay must be protected from weather-driven processes to limit any associated degradation.

Successful prediction of unsaturated soil behavior is quite complex since the simultaneous effects of net stress and matric suction on the degree of saturation and void ratio should be taken into account. Although a large number of constitutive models have been developed to capture the hydromechanical behavior, these models either lack sufficient accuracy to simulate the constitutive behavior of unsaturated soils or are based on complex formulations that affect the accuracy of the results. Therefore, consistent theoretical models supported by efficient algorithms are still needed to understand the hydromechanics of unsaturated soils. In this study, a hydromechanical model based on elasto-plasticity including hydraulic hysteresis has been developed. The proposed model is based on a simpler but powerful mathematical formulation compared to similar models of its kind. The model requires material parameters that require a small number of triaxial experiments to obtain. The study particularly focuses on the effect of the change in void ratio on the water retention behavior. In the integration of the model, an efficient explicit integration algorithm is developed in which a series of unsaturated triaxial tests are simulated at constant suction and constant water content under various net stress and suction traces. Validation analyses have given good results indicating the capability of the proposed model for unsaturated soils.