Long-term mechanical performance of geothermal diaphragm walls in stiff clay

Diaphragm wall equipped with ground heat exchangers is one type of thermo-active foundations, which harness the energy stored by the ground for heating and/or cooling buildings. Past investigations on geothermal diaphragm walls mainly focused on the thermal performance, but paid little attention on their mechanical response to geothermal energy operation. This paper conducts thermo-hydro-mechanical (THM) finite element analyses to investigate the long-term performance of geothermal diaphragm walls in stiff clay. The numerical analyses take account of both the station excavation process in short-term and long-term behaviour of the diaphragm wall. The long-term soil-structure interaction simulation includes three scenarios, examining the effects of ground consolidation, external thermal solicitations and seasonal geothermal operation, respectively. A comparison between the mechanical behaviour of the geothermal diaphragm wall and that of the same wall without geothermal activation indicates that geothermal operation may have an impact on structural serviceability issues (e.g. thermal-induced concrete cracks) although unlikely cause critical safety problems. In particularly, the ground settlement near the station is very sensitive to the stiffness degradation of the stiff clay during geothermal operation, while specific attention should be given to the structural performance at the connections between the wall and slabs due to thermo-induced additional stress concentration.