Investigating the cyclic thermo-mechanical behaviour of an energy pile subjected to combined lateral-axial loading

Abstract:

The growing energy demand in urban areas and increasing environmental concerns have driven the development of new energy technologies. Since the 1980s, energy geostructures—where heat exchanger pipes are attached to geotechnical structures such as foundations—have been developed to provide heating and cooling by extracting or injecting heat into the ground. Among these systems, energy piles have been widely studied due to their thermal behaviour being comparable to that of conventional Ground Source Heat Pump systems, while offering a dual function as both structural elements and energy exchangers. Although existing studies have improved the understanding of the axial mechanical behaviour and energy performance of energy piles, their wider application remains limited by uncertainties in their thermo-mechanical response, particularly under combined axial and lateral loading. This includes the interaction between axial and lateral pile behaviour and the coupling with volumetric thermal loading in the surrounding soil.

This study aims to characterise the effects of combined mechanical and thermal loading on energy piles and to develop open-source, user-friendly design tools that account for thermal cyclic effects. Two complementary approaches are adopted. First, full-scale tests are conducted on two energy piles (0.42 m in diameter and 12 m in length) installed on the campus of École des Ponts et Chaussées. The piles are subjected to a constant axial compressive load corresponding to 30% of their ultimate capacity, while horizontal load is incrementally applied. At each loading stage, thermal cycles with temperature variations of ±10 °C are imposed to simulate operating conditions. Second, the experimental results, together with outcomes from the ANR COOP project, are used to develop a simplified, open-source design tool to support the engineering design of foundation systems incorporating energy piles.

Short bio:

Hello!
My name is Changhao QIU, and I am currently pursuing a PhD, which I began in October 2023. My research focuses on the thermo-mechanical behaviour of energy piles, combining my interest in sustainable energy and geotechnical engineering. Energy piles are an innovative technology that combines the functions of traditional foundation piles with geothermal systems, acting as both structural supports and ground heat exchangers.

My research focuses on understanding the interactions between cyclic thermal and combined mechanical loads in both vertical and horizontal directions. To achieve this, I am conducting real-scale experiments and developing numerical models to study energy pile behaviour under realistic conditions. The ultimate goal is to develop a practical tool that engineers can use to design and optimise energy piles, thereby promoting their adoption as a sustainable construction technology.