Review of the Seismic Response of Immersed Tunnels

Many immersed tunnels are constructed in alluvial formations within earthquake-prone regions, making seismic resistance a critical aspect of their safety design. During an earthquake, tunnel displacements can lead to slippage between the tunnel and surrounding soil, and may be further amplified by liquefaction. This phenomenon can cause severe structural damage, including tunnel flotation. This paper examines the seismic performance of immersed tunnels, starting with an overview of the deformation mechanisms affecting tunnels, including those induced by ground shaking and failure. Given its significance in large foundation deformations and its impact on tunnel integrity, liquefaction is analysed alongside potential mitigation strategies. The seismic design process for immersed tunnels is discussed in detail, covering analytical approaches, numerical modelling techniques (such as finite element and finite difference methods), and physical modelling. Real-world examples are provided to illustrate key concepts. Finally, the paper summarizes the core factors influencing the seismic response of immersed tunnels and highlights future research directions to enhance their resilience in seismic environments.