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.

Current-induced vortex shedding imposes repeated cross-flow loading on offshore wind monopiles, yet its effect on the lateral pile-soil response is not explicitly represented in conventional p-y formulations. This study used a validated three-dimensional ABAQUS model of a large diameter monopile in sand to evaluate static in-line drag, equivalent peak cross flow lift, and stabilized harmonic lift at representative elevations. Static and post-cyclic p-y curves were extracted after up to 10⁴ cycles and compared with the American Petroleum Institute (API) sand relation. The in-line load governed the short-term displacement and bending-moment response, whereas repeated cross flow loading progressively reduced the mobilized soil resistance. After 10⁴ cycles, the reduction reached approximately 6.0–12.5% at z = D/2 and 6.75–13.4% at z = D across the representative low and high load cases. The numerical curves also exhibited a lower initial soil reaction modulus than the API prediction within the investigated shallow zone. A modified p-y formulation was therefore developed by combining a nonlinear depth dependent reference modulus with a cycle dependent degradation coefficient. The formulation provides an engineering representation of VIV-related stiffness degradation for the investigated monopile sand system and loading range.

The use of recycled steel slag and tire-derived rubber as a combined backfill for geogrid-reinforced retaining walls offers a potential resource-recovery route, yet its influence on seismic performance has not been systematically quantified. To address this issue, a two-dimensional nonlinear finite-element model was used to perform 120 time-history analyses for a conventional backfill and nine modified backfills under the El Centro, JiJi, and Kobe ground motions scaled to peak ground accelerations of 0.05–0.20 g. The results showed that increasing the rubber content in the steel slag–rubber composite reduced wall lateral deformation and surface settlement, whereas GZ2 produced the largest wall deformation and XJ20 generated the greatest reinforcement stress in the Kobe-wave case at 0.20 g. When wall deformation, surface settlement, and reinforcement stress were considered together, the composite containing 30% steel slag and 15% rubber particles (GK15) provided the most balanced seismic response, producing the lowest settlement at both monitoring locations while avoiding the pronounced reinforcement-stress increase observed for XJ20; therefore, within the investigated model and seismic-input range, GK15 is recommended as a recycled backfill option for geogrid-reinforced retaining walls.

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.