Numerical study on the thermo-hydro-mechanical behaviour of an energy tunnel in a coarse soil: Fid-Bau Portal

Numerical study on the thermo-hydro-mechanical behaviour of an energy tunnel in a coarse soil

Ma, Chunjing / Di Donna, Alice / Dias, Daniel

Abstract By installing heat exchange pipes in tunnel linings, tunnels can provide energy for heating and cooling of adjacent buildings, while being structurally load-bearing. However, energy production through ground heat exchange induces temperature changes, which can in turn result in additional deformation and stress. This study investigated the coupled thermo-hydro-mechanical behaviour of a tunnel equipped with heat exchanger pipes, accounting for heat transfer, groundwater flow and mechanical response of soil and tunnel lining, through numerical simulations. The proposed model was validated against monitoring data at the real scale available in the literature. The influence of groundwater conditions and ground thermal parameters on the mechanical performance is also investigated. The results under different configurations show that the maximum thermally-induced stress and deformation are within the acceptable range, and the tunnel stability is not affected significantly during a one-year thermal operation cycle. It is shown that the impact of ground thermal properties on the lining internal stress also depends on groundwater conditions. In addition, mechanical responses at the joints between the segments are less affected by thermal activation than the other parts of the segmental lining. The coupled numerical model presented can be further used to better understand the effects of heat transfer, water flow and thermal properties on tunnel structural mechanics during heating and cooling modes, both for safe design and sustainable operation of an energy tunnel system in the long term.