Thermo-Mechanical Performance of a Phase Change Energy Pile in Saturated Sand

Abstract

To reduce the thermal response and improve the heat storage capacity of energy piles, a phase change (PC) energy pile was proposed. This innovative PC pile is made of concrete containing macro-encapsulated PCM hollow steel balls (HSB) as coarse aggregates. A numerical model was developed to simulate the thermo-mechanical behaviors of the PC pile under thermal cycles and sustained loading. The computational model is a three-dimensional model that is symmetrical for the two horizontal directions in geometry. Heat transfer process follows conservation laws of energy. The numerical model was validated by the experiments conducted on the PC pile and the results show that the model can reproduce the major thermo-mechanical effects. Then, the model was used to compare the performance between the ordinary concrete pile and the PC pile in saturated sand under the same experimental conditions, where the piles were considered to be thermo-elastic in nature and the sand was considered as a Mohr–Coulomb elastic-plastic material. The thermo-mechanical response of the PC pile under different thermal loads was analyzed. The results show that at the end of heating, the temperature, strain, and displacement of the PC pile were lower than those of the ordinary pile. As the thermal loading increased, the range of temperature change in the soil around the PC pile increased, as well as the strain and displacement of the pile. The residual strain and plastic displacement after the temperature cycles also increased with the increase of thermal loading. Therefore, when designing phase change energy piles, full consideration should be given to the matching of thermal loads and PC temperature, so as to balance the heat transfer rate of the pile and the thermal response.

A Multiphysics Simulation Study of the Thermomechanical Coupling Response of Energy Piles

“…As the temperature increases, the relative displacement of the soil around a pile also increases, and the energy pile generates additional settlement and unrecoverable axial forces [11][12][13][14]. According to Du Ting, Li Yubo et al [15], as thermal load increases, the temperature fluctuation range of the soil around a pile increases, the strain and displacement of a pile body also increase, and the residual strain and plastic displacement after temperature change also increase. According to Weibo Yang, Laijun Zhang et al [16], under thermal load alone, the displacement of a pile top in the summer can be restored to its original state, and in the winter, an irreversible displacement occurs.…”

Study on the thermal response of spiral energy piles based on field test

“…As the axial constraint increased, the axial thermal stress of the energy pile in clay also increased. To improve the heat transfer effect, bearing capacity, and thermal storage properties of energy piles, many scholars [9][10][11] have started to prepare innovative high-performance concrete as pile materials.…”

Research on Heat Exchange Law and Structural Design Optimization of Deep Buried Pipe Energy Piles

“…The heat exchange effect of energy piles is the key to evaluating whether it can be widely used. At present, many studies have been carried out on the heat exchange of energy piles [10][11][12][13][14][15]. Through the study on the thermal response performance of precast high-strength concrete (PHC) energy piles, it was found that longer heat exchange pipes can positively affect the heat exchange performance of energy piles under peak load conditions [16].…”