Characteristics, causes and control measures of disasters for the soft-rock tunnels in the Wenchuan seismic regions

The Guang(yuan)–Gan(su) Expressway is located in the core areas where the Wenchuan earthquake occurred. The surrounding soft-rocks of several tunnels in this region, such as the Dujiashan and Yangjiashan tunnels, are mainly broken into phyllites due to the severe action of the earthquake. Through analyzing the effects of large deformations, lining damage and collapses, which happen frequently in the soft-rock tunnels in the Guang–Gan Expressway, the characteristics and causes of such geological disasters are obtained. It is demonstrated that the large deformation and collapse occur near the vault and tunnel face. The poor mechanical properties and weak self-bearing capacity of the surrounding rock and the softening caused by groundwater are important contributing factors to these disasters. The lack of experience in the design and construction of tunnels in the meizoseismal area, as well as the aftershocks are other important factors to consider. Field test results indicate that the three-bench and the reserved core soil construction method should be applied to control the stability of broken phyllite tunnels, and that this key technology should be strictly controlled during its construction. In particular, increasing the stiffness of the supporting structure and enclosing of the lining in time are efficient methods to control large deformations and collapses in soft-rock tunnels in the meizoseismal area.