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.

The stress state and density of soil have been considered as the key factors to determine the liquefaction resistance. However, the results of seismic liquefaction case histories, laboratory tests and centrifuge model tests show that the fabric characteristics also influence liquefaction resistance, even more significantly than the contributions of stress state and density. In this study, anisotropic specimens with different consolidation histories were prepared using the 3D Discrete Element Method (DEM) to investigate the influence of fabric characteristics on the mechanical behavior of granular materials and the underlying mechanisms. The simulations revealed that under monotonic shear conditions, horizontally anisotropic specimens exhibited strain hardening and dilatancy characteristics, as well as higher peak strength. Under cyclic shear condition, the normalized liquefaction resistance of the specimens showed a strong linear relationship with the degree of anisotropy, independent of confining pressures and density. Microscopic results indicate that the fabric arrangement aligned with the loading direction leads to the evolution of the mechanical coordination number and average contact force in a manner favorable to resisting loads, which is the underlying mechanism influencing macroscopic mechanical properties. Additionally, the evolution patterns of contact normal magnitude and angle in anisotropic granular materials under cyclic loading conditions were also analyzed. The results of this study provided a new perspective on the macroscopic mechanical properties and the evolution of the microstructure of granular soils under anisotropic conditions.

Frozen soils exhibit unique mechanical behavior due to the coexistence of ice and unfrozen water, making experimental studies essential for engineering applications in cold regions. This review comprehensively examines laboratory investigations on frozen soils under static and dynamic loadings, including uniaxial and triaxial compression, creep, direct shear, and freeze-thaw (F-T) cycle tests. Key findings on stress-strain characteristics, failure mechanisms, and the effects of temperature and time are synthesized. Advancements in microstructural analysis techniques, such as computed tomography (CT), scanning electron microscopy (SEM), nuclear magnetic resonance (NMR), and mercury intrusion porosimetry (MIP), are also summarized to elucidate the internal structural evolution of frozen soils. While significant progress has been made, further efforts are needed to better replicate complex environmental and loading conditions and to fully understand the interactions between multiple influencing factors. Future research should focus on developing novel experimental techniques, establishing standardized testing protocols, and creating a comprehensive database to enhance data accessibility and advance frozen soil research. This review provides critical insights into frozen soil mechanics and supports validating constitutive models and numerical simulations, aiding infrastructure design and construction in cold regions.

In-depth research on the mechanical properties and constitutive models of gas hydrate-bearing sediments (GHBSs) is fundamental for achieving efficient hydrate exploration and geological disaster prevention. In the current study, a bounding surface model for GHBSs is developed based on the principle of thermodynamics. By choosing an appropriate dissipation function and free energy function, a yield surface function containing three shape parameters can be obtained. Considering the filling and bonding effects of hydrates, and introducing the hydrate strength evolution parameter, a thermodynamics-based bounding surface model for GHBSs is established using a non-associated flow rule. Then, the explicit substeping scheme with error control is implemented to develop a UMAT subroutine for the proposed model and integrated into the ABAQUS. Compared with the drained monotonic triaxial shear data indicates that the proposed model can adequately capture the shear behaviors of sandy, silty sandy, and clay-silty GHBSs under different stress levels and saturations. In addition, the model demonstrates good applicability and feasibility in undrained cyclic triaxial shear tests and boundary value problem analysis.

The variability in particle morphology significantly impacts the mechanical properties of rockfill materials. To enhance the understanding of this influence, this study collected basalt rockfill particles from 6 different site sources, with their morphology captured by 3D scanning technology, and then the morphological characteristics categorized through cluster analysis. True triaxial tests for these 6 particle groups were simulated using discrete element method (DEM), and the effects of elongation, flatness, convexity, and intermediate principal stress coefficient on the stress-strain relationship and peak strength were qualitatively assessed through principal component analysis (PCA). Further, by controlling the elongation, flatness, and convexity, 3D reconstructed particle models were created by spherical harmonics (SH) analysis, and the true triaxial tests on these models were simulated to quantitatively clarify the influence of morphological parameters on the macroscopic stress- strain relationship, peak strength, microscopic contact, anisotropic evolution, and other characteristics. Considering the size effect in rockfill materials, multi-scale models incorporating particle morphology were further evaluated across four sample scales. The results indicate that, on the macro scale, the three morphological parameters and the middle principal stress coefficient each have substantial effects on peak strength independently, while the interaction among these parameters does not have a notable influence on the strength. With increasing convexity, the peak strength of samples gradually decreases, while an increase in elongation and flatness leads to a trend of initially increasing and then decreasing strength. On the micro scale, the increase in both elongation and flatness results in a more uniform fabric in the main and lateral directions, while the coordination number shows a trend of initially increasing and then decreasing before stabilizing gradually. The influence of elongation on the main direction fabric is slightly smaller than that of flatness, while convexity has minimal effect on these microscopic features. Additionally, the morphological parameters not only impact the deformation capacity of samples but also demonstrate heightened sensitivity to the strength-size relationship of the sample due to interlocking and boundary constraints between particles. This underscores the pivotal role of morphological parameters in governing the mechanical motion of particles during the sample size scaling process, consequently influencing the strength of the material.

Improper anti-drainage treatment of weakly expansive soil subgrades can lead to significant post-construction deformation and uneven settlement, which severely affect the operational safety and service life of engineering projects. To comprehensively analyze the evolution of soil volume and strength under different hydraulic coupling paths during wetting-drying (W-D) cycles, a loaded W-D cycle testing device was developed. Soil volume was measured during the W-D cycles, and the shear strength and soil-water characteristic curves were analyzed after different cycles. The results indicate that during the W-D cycles, changes in soil volume and strength exhibited distinct stages with similar evolution characteristics. Under the investigated loading conditions, the soil demonstrated significant collapsibility during the wetting process, which gradually diminished as the number of cycles increased. Eventually, the W-D cycles caused the soil to reach an equilibrium state, where its swelling and shrinkage behavior became nearly elastic. At equilibrium state, there is a corresponding void ratio for any moisture content, which is the elastic void ratio (e0el). The e0el is irrespective of the number of cycles and initial dry density. Conversely, higher load and larger amplitude in W-D cycles tend to decrease the e0el. Furthermore, by correlating the unsaturated soil matric suction, secant modulus, and stress path, the volume evolution mechanism of the soil was analyzed based on the soil effective stress theory and pore evolution. The results of this study can serve as a crucial reference point for revealing the deformation mechanism of weakly expansive soil subgrades and selecting appropriate road settlement control methods.

To study the dynamic response rules of pile foundations of mega-bridges over faults in strong seismic areas, a finite element model of the pile foundation-soil-fault interaction of the Haiwen Bridge is established. The 0.2-0.6 g peak acceleration of the 5010 seismic waves is input to study the effect of the seismic wave of different intensities and the distance changes between the fault and the pile foundation on the dynamic response of the pile body. The results show that the soil layer covering the bedrock amplifies the peak pile acceleration, and the amplifying effect decreases with increasing seismic wave intensity. However, bedrock has less of an effect on peak acceleration. The relative pile displacement shows the mechanical properties of elastic long piles. The pile foundation generates a large bending moment at the bedrock face and the upper soil layer interface, and a large shear force at the pile top and the soft-hard soil body interface. The relative displacement, bending, and shear bearing characteristics of the pile foundations on the upper and lower plates of the fault are significantly different. The deformation characteristics are affected by faults in a region ten times the pile diameter. Analysis of the dynamic p-y curves shows that the soil resistance on the pile side of the lower plate at the same depth is greater than that of the upper plate. Sensitivity of the dynamic response of pile foundations on either side of the fault to the effects of seismic intensity and distance between the pile foundation and the fault: distance l > seismic intensity q.

Understanding the temperature-dependent mechanical behavior and fracture characteristics of granite is crucial for many engineering projects. In this study, the real-time temperature curves of granite specimens were obtained during the heating and cooling process, and the thermal treatment tests were conducted. The physical properties of the specimen before and after thermal treatment, including mass, volume, and P-wave velocity, were measured. The acoustic emission (AE) signal in the uniaxial compression is monitored. The results indicate that the physical properties of granite deteriorate with temperature, while the mechanical properties show two effects of thermal strengthening and thermal weakening. This phenomenon is comprehensively analyzed by literature statistical data and optical microscopic observation. Furthermore, the AE characteristic is strongly dependent on temperature. High temperature induces more AE ring count to appear in the early stage of loading. As the temperature increases, the crack initiation stress decreases and the table crack propagation stage becomes longer. The attenuation of high-frequency signals and the enhancement of low-frequency signals are related to the development and interaction mechanism of thermally-induced crack and stress-induced crack. At 600 degrees C, the global b-value increases significantly. Meanwhile, the evolution of dynamic b-value helps explain the failure process of granite under axial load after thermal treatment. In addition, a new thermo-mechanical damage statistical constitutive model of granite considering temperature effects is proposed by introducing AE parameters. The main advantages of this model can well fit the nonlinear behavior of granite in the early loading stage after thermal treatment, and reflect the failure process of granite before the peak value. (c) 2025 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/ 4.0/).

The soil-rock mixture is a heterogeneous material consisting of high-strength rocks and a low-strength soil matrix, with complex interactions among its mesoscopic components under loading. Considering the mesoscopic structural characteristics, the interface between soil and rock, as well as the interior of the soil matrix, are identified as the material's weak points. Using the cohesive model, the initiation, expansion, and fracture of cracks at weak points are described, and a cohesive element insertion program is developed. Subsequently, using the results of direct shear tests, the material parameters for the cohesive elements in the soil matrix and at the soil-rock interface are determined. A mesoscopic numerical method for soil-rock mixtures based on the cohesive model is then established. Based on this, biaxial compression numerical tests on soil-rock mixtures with varying mesoscopic structures were conducted. The influence of different mesoscopic factors on mechanical properties was clarified by analyzing the failure state of cohesive elements. Results indicate that the maximum nominal stress in shear direction of cohesive elements can be determined by the peak shear stress of the load-displacement curve in direct shear tests. The maximum effective displacement is determined by one-fifth of the maximum shear displacement, and the tangential friction coefficient is calculated by the ratio of residual shear stress to normal stress. The numerical method based on cohesive elements can effectively describe the mechanical properties and deformation behavior of soil-rock mixtures, particularly for the strain softening behavior under low confining pressure.