Energy pile groups transmit geothermal energy and have attracted widespread attention as one of new building energy-saving technologies. Accurately predicting the time-dependent behaviors of energy pile groups is a challenge, given the complex thermal and mechanical interactions between piles, surrounding soils and the pile cap. This study presents a semi-analytical solution for analyzing energy pile groups within heat exchangers. Utilizing the transformed differential quadrature method, a flexible coefficient matrix for the saturated surrounding soils is acquired, which accounts for both consolidation and heat transfer. The piles are segmented, and the discrete solving equations considering thermal stresses and expansion are formulated. To accurately reflect the interactions among piles-to-piles, piles-to-soils and piles-to-pile cap, the coupled matrix equations are constructed with involving both the displacement coordination and the force equilibrium at the pile-soil interface as well as the pile cap. The validity of the proposed solution is confirmed through comparisons with results from onsite tests and simulations using COMSOL. Pivotal parameters including temperature variations, pile spacing, and the relative stiffness are discussed through examples. Compared with traditional simulation and field test, the proposed solution enables fast and accurate prediction of displacement and load distribution across pile groups, facilitating the safety evaluation of heat exchangers.

The behavior of soft soils distributed in coastal areas usually exhibits obvious time-dependent behavior after loading. To reasonably describe the stress-strain relationship of soft soils, this paper establishes a viscoelastic-viscoplastic small-strain constitutive model based on the component model and the hardening soil model with small-strain stiffness (HSS model). First, the Perzyna's viscoplastic flow rule and the modified Hardin-Drnevich model are introduced to derive a one-dimensional incremental Nishihara constitutive equation. Next, the flexibility coefficient matrix is utilized to extend the one-dimensional model to three-dimensional conditions. Then, by combining the HSS elastoplastic theory with the component model, the viscoelastic-viscoplastic small-strain constitutive model is subsequently established. To implement the proposed model for numerical analysis, the corresponding UMAT subroutine is developed using Fortran. After comparing the results of numerical simulations with those of existing literature, the reliability of the constitutive model and the program written in this paper is verified. Finally, numerical examples are designed to further analyze the effects of small-strain parameters and viscoelastic-viscoplastic parameters on the time-dependent behavior of soft soils.

Rubber-sand mixtures (RSM), characterized by low unit weight, strong elastic deformation ability, good durability, and high energy dissipation, hold significant potential for civil engineering applications. However, research on the time-dependent dynamic behavior remains relatively scarce, limiting their broader application in practical construction. A thorough understanding of this behavior is critical for ensuring long-term performance of RSM across various engineering contexts. In the study, the effects of rubber's thermal aging and loading history, two key factors of time-dependent behavior, on the dynamic properties of RSM under small to medium strains were investigated. Aging of rubber particles was accelerated through oven aging experiments, followed by resonant column tests to determine the dynamic shear modulus and damping ratio of RSM samples with rubber particles of varying aging levels (5 %, 10%, 15 %, and 20% rubber content). Furthermore, multiple load tests were also conducted on the same samples to assess the impact of loading history on RSM's dynamic properties. The results reveal that thermal aging causes volumetric expansion and a reduction in compressive strength of rubber particles, leading to changes in the dynamic shear modulus and damping ratio of RSM. Specifically, the dynamic shear modulus initially decreases during early aging stages, then increases, eventually stabilizing, while the damping ratio consistently decreases with prolonged aging. With repeated loading cycles resulting in a reduction in dynamic shear modulus and an increase in damping ratio. These results improve our understanding of this composite's long-term behavior and offer practical advice for its use in seismic isolation and geotechnical engineering.

The present study investigated the evolution of the time-dependent behavior of remolded samples of Indian black cotton soil for different loading-unloading-reloading cycles in oedometer conditions. The microstructural analysis was carried out to evaluate the parameters such as particle rearrangement and pore size reduction that are responsible for creep at different time periods. It was observed that micropores existed in large numbers, and the number of pores decreased rapidly with an increase in pore size. The number of pores was found to decrease by 20-30% and 85-90% at the intermediate and final stages of the creep test, respectively. Additionally, it was noted that although small pores and mesopores were less in number, they were significant in pore area calculations. The reduction in pore areas for the intermediate and final stages was found to be in the range of 40-50% and 40-60%, respectively, as there were large proportions of micropores that compressed without influencing the overall pore area. The percentage of vertically aligned particles reduced from 21 to 15% at the end of the test. This observation is attributed to the particle rearrangement and reduction in pore sizes that occurred during the test.

An integrated model that considers multiphysics is necessary to accurately analyze the time-dependent response of hydraulic structures on soft foundations. This study develops an integrated superstructure-foundation-backfills model and investigates the time-dependent displacement and stress of a lock head project on a soft foundation during the construction period. Finite element analyses are conducted, incorporating a transient thermal creep model for concrete and an elasto-plastic consolidation model for the soil. The modified Cam-clay model is employed to describe the elasto-plastic behavior of the soil. Subsequently, global sensitivity analyses are conducted to determine the relative importance of the model parameters on the system's response, using Garson's and partial derivative algorithms based on the backpropagation (BP) neural network. The results indicate that the integrated system exhibits pronounced time-dependent displacement and stress, with dangerous values appearing during specific periods. These values are easily neglected, highlighting the importance of integrated time-dependent analysis. Construction activities, particularly the backfilling process, could cause a sudden change in stress and significantly impact the stress redistribution of the superstructure. Additionally, the mechanical properties of concrete have a significant impact on the stress on the superstructure, while the mechanical properties of the soil control the settlement of the integrated system.

This study investigates the interaction between energy piles and layered saturated soils, considering the consolidation induced by the thermal loads and mechanical loads. Initially, the coupled thermo-hydromechanical solution of layered media is obtained by utilizing the boundary element method (BEM) and the transformed differential quadrature method. Subsequently, the energy piles are discretized and modelled by the finite element method (FEM), and the solving equation for piles is established. To reflect the interaction between piles and soils, a coupled BEM-FEM matrix equation is formulated and solved by incorporating displacement coordination conditions and force equilibrium conditions. This approach facilitates the analysis of the temporal evolution of displacements and temperatures of piles and surrounding soils. The proposed methodology is validated through comparisons with monitoring data of field tests and results from simulations. Ultimately, the key factors, including the temperature increments, mechanical loads, length-diameter aspect ratio are examined through examples.