|Abstract: ||The effect of temperature on the behaviour of soils is a crucial problem in geothermal engineering as soils are subjected to the action of temperature variation in many diverse conditions. It is observed in both laboratory experiments and in situ tests that temperature variations can induce interaction between the thermal, hydraulic and mechanical behaviour of soils, which is known as thermo-hydro-mechanical (THM) coupling.
In order to simulate the THM coupling, it is necessary to combine the equations governing heat transfer through the soil mass with the equations governing pore fluid flow through the soil skeleton, and the equations governing the stress-strain behaviour of the soil. Due to the complexities of the governing equations, the finite element (FE) method has been regarded as an appropriate numerical tool to solve THM coupled problems. In this thesis, all of the research has been carried out using the Imperial College Finite Element Program (ICFEP), which has been developed specifically for geotechnical engineering analysis.
This thesis develops the governing equations for THM coupled analysis. It then describes the implementation of these equations for fully saturated soils in ICFEP. This theory has been applied to all types of elements in ICFEP, such as solid, beam, bar, joint, membrane and shell elements. Thermal boundary conditions relevant to geotechnical engineering have also been developed and implemented into ICFEP. A series of validation tests on the new facilities has been performed, and the results have been compared to those obtained using analytical and finite difference methods.
To avoid numerical oscillations, the time-step constraints in coupled transient FE analyses, as well as an adequate mesh discretisation in highly convective coupled analysis, have been investigated. The findings from the analytical and numerical studies have been applied to a simulation of an open-loop ground source energy system, and the results show an excellent agreement with the available approximate solution.|