Damage observation and assessment of the Longxi tunnel during the Wenchuan earthquake

• We describe in detail the damage observed at the Longxi tunnel cross a fault zone.
• Serious damage and even collapse of the tunnel occurred close to the faulted zone.
• We present a detailed 3D numerical model to determine the mechanisms of damage.
• We discuss effects of seismic input directions and the fault on the tunnel damage.
• The longitudinal seismic motion has a significant effect on tunnel performance.

The Longxi tunnel was one of the most damaged tunnels during the 2008 Wenchuan earthquake in China. What makes the case interesting is that the tunnel crosses a fault zone. Damage from small to heavy cracking was observed both at the portal and inside the tunnel, while sections close to the fault completely collapsed. A full three-dimensional dynamic finite element model of the tunnel and rock system is used to assess the seismic damage observed in the tunnel and to evaluate the influence of the longitudinal and vertical motions on the seismic response. A comparison between the numerical predictions and the damage reported shows a good agreement. The results indicate that the longitudinal earthquake motion has a significant effect on the response of the tunnel structure and should be considered for the structural design of tunnels in seismic zones. In contrast, the vertical seismic motions can generally be neglected.