Hydraulic influences on the long-term performance of tunnels: A review

Long-term performance of tunnels usually depends on their interaction with surrounding environment induced by various internal and external, natural and anthropogenic factors. Understanding these long-lasting impacts is paramount and crucial for the sustainable lifelong management of tunnel infrastructures. Considering prolonged rainfall, sea level rise and other extreme geohazards partly due to climate change, this paper specifically reviews previous studies examining the hydraulic influences on the long-term performance of tunnels. The variation in groundwater levels, changes in the hydraulic permeability of the surrounding ground and tunnel linings, water leakage, and tunnel deterioration are key hydraulic factors that critically affect the long-term performance of tunnels. The primary objective is to identify research gaps and limitations and provide insights for future research directions to improve our understanding of the long-term performance of tunnels under hydraulic influences. It is found that previous studies often fail to quantify these effects, exemplified by subjectively varying groundwater levels, ground and tunnel permeability and assuming random distribution of tunnel deteriorations. Therefore, future research should focus on adopting laboratory/field data-based, realistic assumptions, aiming to advance the understanding of the performance of tunnels across their lifespan and eventually enhance the principles of tunnel design, construction, and maintenance.