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  Dynamic response of tunnel portals in mountainous areas with High seismic activities

  Many portal structures of tunnels in mountainous area have been severely damaged during strong earthquakes in recent years, especially in the Wenchuan earthquake. This paper analyzes the dynamic responses of tunnel portal structures using three dimensional (3D) Finite Difference Method (FDM) for a real highway tunnel in Wenchuan area. The deformation characteristics and stress behaviour of the tunnel portal structure was numerically simulated through a 15-second seismic wave period. It was found that the tunnel structures at diagonal directions are subjected to tensile and compressive deformations during the seismic motion, corresponding to the seismic damages at tunnel upper-structures and bottom sidewalls. Even though the principal stresses at various monitoring points generally reach their peaks at different times, the points at tunnel diagonal directions tend to the maximum tensile and compressive stresses simultaneously. It is also identified that the damage to the tunnel upper-structure is generally caused by excessive relative displacement of lining, while the damage of bottom sidewalls is normally caused by structural principal stress. In addition, a large-scale shaking table laboratory test was performed to validate the damage locations and crack distributions of lining under strong seismic motion.

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