Numerical modelling of ground settlement induced by long-term operation of an energy tunnel

Abstract

Energy tunnels are innovative geotechnical facilities to make use of shallow geothermal energy. Although this technology is getting increasingly popular, the behaviour of energy tunnels is still not fully understood. The coupled thermal and mechanical loading conditions of the energy tunnel pose several challenges for geotechnical engineers. Most of the existing studies only focus on the thermal performance of energy tunnels, while the thermo-mechanical response is still investigated in the literature rarely, especially the serviceability limit state of energy tunnels. Regarding the thermo-mechanical behaviour of soil, there are quite a few experimental studies and several advanced constitutive models proposed. However, none of them have been applied to the research of energy tunnels. In this research, a thermodynamic based advanced constitutive model is implemented into a commercial finite element software COMSOL. A coupled thermo-mechanical model is developed for energy tunnels under long-term cyclic thermal loading. A 10-year heating-cooling operation of the energy tunnel is simulated. Temperature variation induces volume change of soil, leading to accumulated ground settlement eventually. Without a full consideration of the thermal response of soil, the traditional numerical approach may not be conservative enough when evaluating the serviceability of energy tunnels.