Double-deck tunnels beneath the groundwater table have relatively large volume and commonly constructed as watertight tunnels. In this case, it requires to secure stability of the tunnels for buoyant force. Generally the contact force between lining and ground is sufficient to resist the buoyant force. However in the long-term the contact force could be reduced because of structural deterioration. In this study the effect of long-term buoyant force acting on the double-deck tunnel is

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... d. The results has shown that the buoyant force has increased invert deformation and stress. It is indicated that the contact resilience between lining and ground needs to be kept during tunnel operation.