Synergistic Effects of Humidity and Vibration on Tunnel Segment Degradation

Compared with above-ground structures, tunnel structures are subjected to a much more complex engineering environment. Their structural systems and materials must not only withstand long-term dynamic loads, such as train-induced vibrations, traffic loads, and seismic loads but also endure high groundwater pressure and the gradual deterioration caused by acidic water penetrating the concrete. These factors can generate independent deterioration of tunnel segments, while the coupling effect can accelerate the deterioration process even further [Eng et al. 2019].

First, mechanical actions occur when tunnel vibrations are induced by multiple dynamic sources, such as ground traffic loads, earthquakes, train operations, and resonance effects between the surrounding soil and the structural system. These actions lead to the development of microcracks in the tunnel lining or even more severe damage on the concrete surface. Second, groundwater infiltration triggers several key mechanisms that affect the tunnel lining. The microcracks allow further water ingress, which in turn causes steel reinforcement corrosion and ultimately results in a gradual degradation of overall material performance. Once the above structural deterioration processes become cyclic, the deterioration is no longer driven by a single factor but is instead accelerated by the coupled interaction of multiple mechanisms.

Therefore, addressing tunnel segment deterioration based solely on analyses of a single mechanical or environmental factor is insufficient. The coupled interaction between hydro-chemical actions (e.g., water ingress and corrosion) and mechanical actions (e.g., vibrations) gives rise to complex multi-physics deterioration processes. This process promotes crack propagation and the progression of reinforcement corrosion. To overcome the aforementioned deterioration cycle, a structural systems level is required to analyze the coupled effects of materials science, structural dynamics, and environmental engineering on underground structures. The scope is to enhance the long-term durability and safety of tunnel structures.

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