Accurately predicting pile load–displacement behavior is critical for optimizing deep foundation design and ensuring structural safety. Traditional empirical and numerical methods often fall short in capturing the complex, nonlinear interactions among pile geometry, soil resistance, overburden stress, and applied load under varied site conditions. To address these limitations, this study introduces a hybrid machine learning framework that integrates Moth–Flame Optimization and Tree-structured Parzen Estimator for hyperparameter tuning of the eXtreme Gradient Boosting algorithm. The model is trained on a comprehensive database of 2828 static load test results from real-world projects in Vietnam, including bored piles (1650 samples) and prestressed high-strength concrete driven piles (1178 samples). Pile type is explicitly considered to account for differences in load-bearing resistance mobilization. The proposed model demonstrates superior predictive performance (R² = 0.979, root mean squared error = 5.043 mm, mean absolute error = 2.860 mm). Sensitivity analysis reveals several geotechnical thresholds associated with variations in pile settlement. Partial dependence plots indicate that the standard penetration resistance below the pile toe consistently influences displacement, where values exceeding 35 blows per 0.3 m are associated with significantly reduced settlement. In contrast, piles embedded deeper than 60 m in weak soils—with penetration resistance below 35—may exhibit increased displacement due to limited side friction and inadequate toe mobilization. Overburden stress at greater depths also shows a more consistent contribution to settlement reduction than shallow confinement, underscoring the importance of deep-layer properties in load transfer. These findings provide actionable insights for serviceability-based design, enabling more efficient and reliable foundation solutions. The model’s robustness is further validated through pile-type-specific evaluation and Monte Carlo-based uncertainty propagation. Overall, the proposed framework offers a scalable, interpretable, and cost-effective solution for advancing data-driven pile foundation engineering.

The full skin friction and full end-bearing resistances of a single pile are not mobilized at the same displacement, while the conventional approach often oversimplifies by adding the skin friction to the end-bearing resistance as independent calculation steps. This paper presents a simplified interaction approach for the nonlinear load–settlement analysis of a single pile considering simultaneously the degradation of skin friction resistance and end-bearing resistance hardening under varying loads. The ability to estimate the load–settlement response of piles based on either needed loads or settlement is a special benefit of the proposed approach over existing methods. In addition, the proposed model is able to separate the skin friction resistance, end-bearing resistance, and elastic compression at arbitrary settlement. The analytical method shown a satisfactory performance as compared to experimental results for three extensively studied field test situations. The suggested approach shows promise as a suitable solution for the design optimization as well as the preliminary analysis to organize a suitable loading test program. A parametric analysis is conducted to further examine the influence of various significant parameters related to the load–settlement response of piles.

Energy piles are a dual-purpose geostructure system designed to serve both as load-bearing foundations and as a means of utilizing geothermal energy for heating and cooling buildings. Due to their dual function, the behavior of energy piles under temperature variation at the pile–soil interface is significantly more complex than that of traditional piles. This study proposes a unified method for predicting the load–settlement behavior of traditional and energy piles, formulated through a cubic equation that integrates end-bearing hardening, skin-friction softening, and a modified effective stress theory accounting for particle contact area evolution. Unlike existing approaches, the proposed method uniquely separates end-bearing and skin-friction resistances and captures the coupled thermal-mechanical effects at the soil–pile interface, including both resistance gains and losses due to heating or cooling. Validation against interface shear tests and full-scale field measurements confirms the accuracy and robustness of the proposed method. Results show that the proposed framework significantly improves load–settlement predictions and provides a physically consistent and practical tool for energy pile design under varying thermal and mechanical loads. The findings also highlight that temperature effects on energy pile resistance vary with soil conditions. Heating can increase resistance via pile expansion, radial thermal stress, higher particle contact, and friction angle. Conversely, it may reduce resistance due to thermally induced excess pore-water pressure, lower overconsolidation, total stress reduction, decreased stiffness, and cohesion loss. These opposing mechanisms highlight the complex, site-specific thermomechanical behavior of energy piles. Considering microstructural evolution and thermal-softening effects is necessary to enhance the predictive capabilities for pile performance in complex operational environments.

Climate change has intensified rainfall variability, droughts, and temperature extremes, amplifying the risks of instability and deformation in geotechnical infrastructure. Traditional saturated soil frameworks are inadequate to capture these effects, whereas unsaturated soil mechanics (USM) offers a more realistic basis for understanding soil behavior under fluctuating hydro-climatic conditions. This paper reviews the critical role of USM in advancing climate-resilient geotechnical engineering. Key challenges include the complexity of soil–atmosphere exchanges, hydraulic hysteresis, scaling from laboratory to field, and uncertainty in climate projections. Concurrently, opportunities are emerging through advanced monitoring, innovative experimental techniques, computational modeling, climate integration, and reliability-based design. By extending classical bearing capacity models, this study integrates USM to more accurately predict geostructure performance. Analytical insights, supported by case studies, demonstrate the influence of rainfall-induced infiltration on slope stability, shallow foundation capacity, and column-supported embankments. Results reveal that suction enhances soil strength but may diminish rapidly during infiltration, heightening failure risk. The study advocates embedding USM into design codes, modeling frameworks, and early-warning systems to move from reactive to proactive resilience. Bridging theory and practice, it provides a pathway for adapting geotechnical systems to climate variability and ensuring long-term infrastructure durability.

The study and application of soil arching theory in geosynthetic-reinforced pile-supported (GRPS) embankments have gained increasing attention, as accurate arching estimation significantly influences load-deflection behavior of structures. While most existing models rely on Rankine's earth pressure theory, which applies primarily to granular soils and neglects cohesion effects. This paper employs three-dimensional numerical simulations to examine the impact of soil cohesion on soil arching mechanisms in pile-supported embankments. Results indicate that cohesion enhances load transfer to piles, with arching efficacy increasing nonlinearly before stabilizing at higher cohesion values. Building on these findings, the ground reaction curve (GRC) model is proposed to predict arching behavior in both cohesive and non-cohesive embankments at various deformation stages. By integrating critical state soil mechanics with the concentric arch model, the transition between maximum and critical arching states is captured through changes in the mobilized friction angle with relative displacement. Model validation against two well-instrumented case studies demonstrates its accuracy, particularly in accounting for soil cohesion. Moreover, the maximum arching model better predicts GRPS embankments under small deformations (relative displacement <4 %), while the critical arching model is more suitable for large deformations (relative displacement >6 %). The proposed model effectively captures arching behavior improvements in both cohesive and non-cohesive soils.

One of the most crucial tasks in the design, control, and construction of urban deep excavations is ensuring the safety of the existing underground infrastructure. Deformation and settlement created by excavation may damage the adjacent tunnels. In this study, the stability of an existing triple tunnel in relation to the construction of an adjacent deep excavation is evaluated by numerical simulation using both the discrete-element method (DEM) and the finite-element method (FEM). A deep excavation supported by the retaining wall and five levels of strutting system was created adjacent to an existing triple tunnel. The excavation’s width and depth were 30 and 16 m, respectively. In both discrete-element (DE) and finite-element (FE) simulations, the horizontal spacing of the triple tunnel wall relative to the retaining wall (SH) is varied between 3 and 35 m, while vertical spacing of the triple tunnel’s crown from the ground surface (SV) is changed from 4.8 to 32 m. The results indicated that at a certain value of SV and with increasing the SH, the horizontal displacement of the wall decreases. The variations in the triple tunnel position significantly affected the settlement pattern. In addition, the results showed that the maximum vertical displacement occurred at the middle tunnel crown, while the lowest value of the maximum vertical displacement was found at the crown of the right tunnel. At a certain value of the vertical displacement, the wall horizontal displacement is deduced by increasing in the SH value.

The partial factor method is the most common approach to verify structural safety in Eurocode 7. Given the ongoing discussion on the European level to include also underground excavations in rock in the scope of the Eurocodes, there is a clear need to investigate the applicability of partial factors to the design of rock tunnels. However, implementing fixed partial factors, in accordance with the suggestion in the current Eurocode 7, may not be appropriate to account for the large uncertainties and variable conditions prevalent in rock engineering. This paper studies the critical characteristics and underlying assumptions of different reliability-based partial factor formats. The suitability of the analyzed partial factor formats to evaluate safety is analysed and discussed with reference to a design example of a rock-shotcrete interaction system for support against block failure in an underground opening. The results show that reliability-based partial factor methods outperform the traditional partial safety format suggested in the Eurocode in terms of accuracy and consistency.

Due to the relatively different mechanical and physical properties of soils and structures, the interface plays a critical role in the transfer of stress and strain between them. The stability and safety of geotechnical structures are thus greatly influenced by the behavior at the soil–structure interface. It is therefore important to focus on the unique characteristics that set the interface apart from other geomaterials while examining the interface behaviour. Understanding the physical mechanism and modelling principles of these interfaces becomes a crucial step for the secure design and investigation of soil-structure interaction (SSI) issues. Moreover, to deal with this soil-environment interaction problem, the classical soil mechanics formulation must be progressively generalised in order to incorporate the effects of new phenomena and new variables on SSI behaviour. Considering the variety of energy geostructures that are emerging nowadays, it is crucial to comprehend the thermo-hydro-mechanical (THM) behaviour of the interface. The objective of this study is to fill this information gap as concisely as possible. A critical review is provided along with the state-of-the-art information on the thermo-hydro-mechanical behaviour of the soil-structure interface, including testing tools and measurement methods, basic principles and deformation mechanisms, constitutive models, as well as their applications in numerical simulations. This study explains how loading influences the mechanisms at the interface and critically examines the effects of boundary conditions, soil properties, environmental factors, and structure type on the THM behaviour of interface zones between soils and structural elements. The validity and reliability of the interface shear stress-displacement models are also covered in this paper. Lastly, the trends and recent advancements are also recommended for the interface research.

This work presents a simplified method for the nonlinear analysis of the load–displacement response of piles in multi-layered soils. As a starting step, a new interface model based on the disturbed state concept (DSC) is put forth to simulate the interface shear stress-displacement relationship by considering the nonlinear hardening–softening behaviour. In the new model, input parameters can be conveniently calibrated using conventional interface shear tests or on-site tests. The good agreement between predictions and experimental data from interface direct shear tests validated the performance of the proposed DSC model. The DSC model performed better in terms of predictions when compared to the hyperbolic one. Next, the soil-structure interface model and bearing capacity theory are coupled to provide a theoretical framework for the analysis of pile load-transfer in saturated and unsaturated multi-layered soils, where the DSC model is employed to represent base resistance as well as skin friction. This work also discusses the profile of steady-state in-situ matric suction, soil–water characteristic curve, and pore-water pressure of unsaturated soils. The proposed method has the advantage of being used in practice as it is simple to obtain input parameters from laboratory tests, as well as Standard Penetration or Cone Penetration Tests. The proposed framework is finally applied to the analysis of five well-documented case studies. The proposed approach and the static load test results from the field measurements are found to be in satisfactory agreement, indicating that the proposed method performs well. The proposed method is suggested to be utilised for preliminary analysis, planning a suitable programme of loading tests, as well as optimizing the pile design by back analysis of the load test results.

The bearing resistance of energy piles in the presence of temperature effects has not been thoroughly investigated, preventing the perfecting of energy pile design methods. Quantifying the relationship between soil suction and the temperature of unsaturated soils therefore becomes an important step in predicting the bearing resistance of energy piles. A new constitutive model based on interfacial energy and thermodynamic theories is therefore presented to predict the effect of temperature on soil suction as well as the soil–water characteristic curve (SWCC) in this paper. The analytical model for the nonisothermal matric suction was developed by combining five different temperature-dependent functions for the surface tension, air–water contact angle, void ratio, and thermal expansion of solid and water density, thereby providing a more complete approach than the one that considers surface tension only. The proposed formulation was expressed under a simplified form which is believed to be a useful and convenient tool to apply to a range of possible field situations. The temperature-dependent relationship of soil suction was then used to extend existing isothermal SWCCs to nonisothermal conditions that allow obtaining the SWCC at any temperature. The validity of the proposed model was verified by comparison to several test data sets for five different soils: swelling clay, hard clay, clayey–silty soil, ceramic material, and sand. The satisfactory agreement between predicted and measured curves proved that the proposed model had good performance in predicting the effect of temperature on the SWCCs of unsaturated soils. The nonisothermal SWCC model was then coupled with bearing resistance theory to produce a simplified method for analysis of energy piles. The results showed that the proposed method successfully predicted pile resistance at various temperatures when compared to experimental data. The pile resistance reduced as the temperature rose for a specific degree of saturation or if the soil was in an undrained condition. However, water evaporation may cause a decrease in water content and an increase in matric suction as the temperature increases. Therefore, as soils dry out, pile resistance may increase with increasing temperature.