Thermo-active piles have gained popularity in recent years due to their dual role of providing structural stability as foundations and exchanging heat with the ground as ground source heat exchangers to provide low carbon heating and cooling. The installation of thermo-active piles is further facilitated by the enforcement of sustainability targets, such as the Merton Rule, which requires a proportion of the energy demand of a building to be met by renewable energy generated on site. When thermo-active piles operate and are, therefore, subjected to changes in temperature, the existence of a temperature field and the resulting thermal expansion and contraction of materials induces a complex thermo-mechanical response.
The objective of the research presented in this thesis is to investigate the thermo-mechanical behaviour of thermo-active piles when they are subjected to changes in temperature, which can be due to the heat of hydration generated when they are cast, or their operation. This is achieved by performing fully coupled thermo-hydro-mechanical (THM) finite-element (FE) analyses using the Imperial College Finite Element Program (ICFEP). In order to simulate accurately the thermo-mechanical behaviour of thermo-active piles resulting from their operation, three-dimensional (3D) analyses are carried out where the heat exchanger pipes are explicitly modelled. However, these analyses are computationally expensive that render them impractical to perform in routine engineering design. A simplified method to model the problem using only two-dimensional (2D) analyses is developed. To model accurately the amount of heat generated from the hydration of concrete, a simple concrete heat of hydration model is developed, which can be readily applied in geotechnical applications.
The aforementioned developments ultimately allow the identification of whether the critical stage in terms of thermo-mechanical behaviour of a thermo-active pile is during its hydration or operation.