The impact of thermal-hydraulic variation on tunnel long-term performance: a tale of two tunnels

Long-term structural performance of ageing tunnels is influenced by various natural and anthropogenic factors. This study examines the impacts of two rarely-investigated climatic factors: rainfall and temperature. Two dedicated case studies were conducted on the CERN TT10 tunnel and Dublin Port Tunnel (DPT) using distributed fibre optic strain sensing (DFOS) and wireless sensor network (WSN) monitoring respectively. DFOS data showed an increasing deformation in TT10 tunnel, attributed to tunnel deteriorations and ground deformation, with seasonal variation of lining strains linked to rainfall-related seasonal change in pore water pressure. However, inconsistencies in rainfall-strain correlation were also noted due to geological complexities and varying pore water pressure sources. In contrast, WSN measurements showed that DPT deformation correlated with temperature, instead of precipitation. DPT deformation increased in warmer seasons and decreased in colder ones, in the absence of external disturbances, comprising reversible thermal deformation and irreversible deterioration-induced deformation. Over time, cyclic and periodic temperature changes caused elastic deformation to reverse, while plastic deformation accumulated, leading to ongoing tunnel deformation. These findings bring more insights into the resilience of critical underground infrastructure vulnerable to climate change, groundwater variations, and other environmental factors.