Damage mechanism and optimization design of wall-type portal tunnels underseismic action: Seismic damage investigation and a theoretical model

Abstract The deformation incompatibility between the wall-type portal and the tunnel lining during seismic events is a significant contributing factor to damage at tunnel portal. Recognizing the lacuna in theoretical analysis methods for assessing seismic damage in wall-type portal tunnel, this study develops a theoretical model, which simplifies the wall-type portal as a concentrated mass and represents the lining as a Timoshenko beam, thereby establishing a analytical model for evaluating the longitudinal dynamic response of wall-type portal tunnels. The Green's function method is employed to derive an analytical solution, and the validity is corroborated by numerical simulations. A systematic exploration of wall-type portal tunnel parameters is conducted on the tunnel dynamic response. The results reveal that an excessively large portal mass or insufficient portal foundation stiffness can induce a displacement amplification effect at the tunnel portal section; conversely. These theoretical analysis results effectively validate the potential seismic hazards and associated mechanisms specific to wall-type portal tunnels. Key strategies to enhance the seismic performance of wall-type portal tunnels include: (1) optimizing the mass or geometry of the wall-type portal to promote coordinated deformation with the tunnel lining; and (2) implementing seismic isolation measures to effectively mitigate interaction forces between the portal and the soil. • The damage survey identified four seismic failure modes for wall-type portal tunnel: (i) overall portal failure due to soil-portal interaction; (ii) contact crushing failure between the portal and the lining; (iii) contact tension failure between the portal and the lining; and (iv) bending or shear failure of the tunnel lining induced by forces exerted by the portal. • A novel analytical solution for the longitudinal dynamic response of the wall-type portal tunnel is derived, facilitating analysis of the interaction between the surrounding rock, the portal, and the lining. • A systematic exploration of the influence of portal structure parameters on the dynamic response of the tunnel structure is conducted based on the analytical solution.