Damage to mountain tunnels related to the Wenchuan earthquake and some suggestions for aseismic tunnel construction

Many tunnels along the Dujiangyan to Wenchuan highway, located near the epicenter of the 2008 Wenchuan earthquake in China, were damaged severely. The characteristics of the tunnel failures were analyzed and categorized as avalanches and landsliding near the tunnels, cracking of the tunnel portals, collapse of the liner and surrounding rock, cracking and dislocation of the liner, uplift and cracking of the ground, deformation and cracking of the preliminary bracing. The main geological factors influencing the tunnel damage are secondary fractures of earthquake faults, sudden change in soil and rock type, weak rocks and the variable geo-stresses in the host material. The tunnel portals and their slopes, unless fully integrated into the tunnel structures and sufficiently reinforced, are likely to suffer significant distress as a consequence of seismic events. The main mitigation measures proposed are the use of reinforced concrete in the secondary lining in the area of fault zones and injection grouting to reduce the differences where there are sudden changes in the character of the host material.