Freeze-sealing pipe roof method is applied in the Gongbei tunnel, which causes the ground surface uplift induced by frost heave. A frost heaving prediction approach based on the coefficient of cold expansion is proposed to simulate the ground deformation of the Gongbei tunnel. The coefficient of cold expansion in the model and the frost heaving rate from the frost heave test under the hydration condition can achieve a good correspondence making the calculation result closer to the actual engineering. The ground surface uplift along the lateral and longitudinal direction are respectively analyzed and compared with the field measured data to validate the model. The results show that a good agreement between the frost heaving prediction model and the field measured data verifies the rationality and applicability of the proposed model. The maximum uplift of the Gongbei tunnel appears at the center of the model, gradually decreasing along with the lateral and longitudinal directions. The curve in the lateral direction presents a normal distribution due to the influence of the constraint of two sides, while the one along the lateral direction shapes like a parabola with the opening downward due to the temperature field distribution. The model provides a reference for frost heaving engineering calculation.

The energy pile integrates shallow geothermal energy extraction with underground structural engineering, thereby expanding the functional applications and scope of pile foundations. Due to its widespread adoption, research on energy pile analysis theory has advanced significantly. Among existing analytical methods, the load transfer method is widely employed owing to its computational simplicity and readily obtainable parameters. However, current load transfer models for energy piles remain imperfect, primarily because their results often fail to accurately reflect real-world loading conditions. This study investigates the underlying causes of this discrepancy and proposes an iterative method to eliminate unbalanced forces at the pile head, based on the displacement coordination algorithm for energy pile load transfer. The calculated results at the pile head show an 18% reduction in error compared to previous studies. The average error compared with field test results is within 20%, with consistent trend patterns, confirming the feasibility of the proposed method. Computational results demonstrate that the proposed method effectively captures the combined effects of mechanical load and temperature variations on the bearing behavior of energy piles. It should be noted that this paper focuses specifically on improving the temperature-dependent load transfer method for energy piles. Consequently, the conventional load transfer method and results under purely mechanical loading are not discussed herein.

This paper presents an experimental investigation on the undrained strength and stress–strain response of saturated silt using a temperature-controlled triaxial apparatus. A series of consolidated undrained triaxial compression tests were performed on saturated silt. Prior to shearing, the normally consolidated specimens were heated or subjected to a heating–cooling cycle in a temperature range of 20–60 °C. The undrained stress–strain and excess pore pressure responses at various consolidation pressures and temperatures are analyzed. The effects of heating and heating–cooling cycle on undrained strength are emphasized. The temperature effect on the phase transformation behavior and critical state is revealed. The results show that (1) the Nanjing silt presents an obvious phase transformation behavior, which is affected by temperature. A unique critical state line at various temperatures can be observed; (2) the undrained strength is increased by heating and heating–cooling cycle. The normal consolidated silt exhibits dilation behavior and hardening stress–strain response; (3) the pore pressure is accumulated by an undrained heating–cooling cycle, and it nonlinear increases with temperature; (4) the change of normalized undrained strength relies on the overconsolidation ratio (OCR) and temperature.

This paper presents a simple thermo-elasto-plastic constitutive model for saturated fine-grained soils, addressing thermal volume change, excess pore pressure, and shear strength. The model incorporates a novel temperature-dependent plastic modulus formulation that attributes the thermoplastic strain to an internal state variable representing the thermal stabilization of soils due to cyclic thermal loading. It can capture the accumulative volume expansion of highly overconsolidated (OC) soils, and the accumulative contraction of normally consolidated (NC) and slight OC soils after several heating–cooling cycles. A thermally induced pore pressure formula is derived with consideration of thermo-elastic expansion of pore water and soil particles, thermo-plasticity of soil skeleton as well as the elastic unloading due to the decrease of effective stress under undrained heating. The effect of temperature on the shear strength was emphasized. An insight into the evolution of shear strength with temperature is provided. The consolidated stress history and stress path play a vital role in the thermal effect on the shear strength. The proposed model comprises nine parameters, which can be easily calibrated by element tests (triaxial tests and oedometer tests). The adequacy of the proposed model has been verified with experimental results from fine-grained soils documented in the literature.

Energy piled raft foundations require the mechanical response of the raft, piles and surrounding soil to be evaluated together with temperature-induced pile deformation. Field testing is often costly, whereas full three-dimensional finite element analysis can impose a substantial modelling and computational burden. This study presents an elastoplastic analytical framework for conventional piled rafts and energy piled rafts under mechanical and thermo-mechanical loading. The framework idealizes the raft as a thin plate, the piles as one-dimensional compression members and the foundation soil as an interaction medium described by Winkler-type support and Mindlin-based flexibility formulations. Raft-soil-raft, pile-soil-pile and raft-soil-pile interactions are assembled into a global stiffness system. Elastoplastic shaft and base resistances are updated through an incremental solution scheme, and thermal loading is introduced as equivalent nodal forces generated by pile temperature variations. The method is implemented in an object-oriented C++ program and evaluated through four benchmark problems, including conventional piled rafts under mechanical loading and energy piled rafts under coupled thermo-mechanical loading. The predictions are compared with classical analytical solutions, field measurements and published finite element results. Across these comparisons, the proposed framework captures the load-settlement response of conventional piled rafts and the axial load redistribution of energy piles, including the development of neutral-plane-controlled load accumulation and release along the pile shaft. These results support the applicability of the method for analysing load transfer in complex pile-raft systems while retaining a lower modelling burden than full three-dimensional finite element analysis.

Energy pile technology integrates geothermal energy exploitation with pile foundation bearing, yet accurately evaluating its thermo-mechanical performance remains theoretically challenging. To address the limitations of traditional load-transfer methods for accurately locating the neutral plane—which cause inconsistencies between computed pile-head axial forces and applied loads, and calculation discontinuities at the neutral plane—this study proposes an improved method using an iterative algorithm to eliminate unbalanced forces. Furthermore, based on a non-linear load-transfer function for pile-soil displacement compatibility, a model with well-defined parameters is established to capture the impact of long-term temperature cycles on the evolution of shaft resistance. A comprehensive calculation method for pile axial force and shaft resistance under cyclic temperature effects is thereby established. The analytical method is systematically validated against classical numerical methods and field test data from the London and Kunshan energy piles. Subsequent analysis reveals that heating–cooling cycles induce additional pile settlement. With increasing thermal cycles, the pile’s mechanical response evolves and ultimately stabilizes. Finally, increasing the applied mechanical load progressively attenuates the impact of cyclic temperature variations on the pile’s load-bearing performance.