Numerical modelling of thermo-active retaining walls

Abstract

The exploitation of the energy stored in the ground through geotechnical structures poses new challenges to geotechnical engineers due to effects related to temperature changes that have to be considered in the design of these structures. Underground structures, such as piles, retaining walls or tunnel linings, can be equipped with heat exchanger pipes through which thermal energy is exchanged with the ground to provide low-carbon space heating and cooling. The exchange of energy imposes temperature changes to the structure and the ground, which can induce additional stresses and strains within the structures, as well as leading to thermo-hydro-mechanical (THM) interactions within the ground. The research presented in this thesis focuses on the analysis of these phenomena in relation to the utilisation of retaining walls as heat exchangers, also termed thermo-active retaining walls. The aim of this research is to assess the impact of temperature variations on the behaviour of thermo-active retaining walls and the surrounding soil and to provide efficient modelling approaches for their design. In recent years, the Imperial College Finite Element Program (ICEFP) has been upgraded to include a fully coupled THM formulation for saturated soils as well as special types of elements for the simulation of the heat exchanger pipes, allowing the simulation of complex boundary value problems including thermo-active structures. Firstly, the phenomena taking place within the soil when temperature changes are applied are analysed in detail to provide the basis for the assessment and interpretation of the performance of thermo-active retaining walls. Subsequently, modelling approaches for the accurate simulation of the pipe-structure-soil interaction within three-dimensional analyses of thermo-active retaining walls are established and validated against field data. The findings are employed to develop simple and computationally efficient modelling approaches to simulate thermo-active walls in two-dimensional analyses, focussing both on their energy efficiency and structural behaviour.