Abstract: The selection of an appropriate advance support type in the shallow buried tunnel portal in the mountain should both consider the construction cost and the safety as well as the risk during the construction. In the construction of the Zhaizibao Tunnel in Fanba Jiangbei Highway Project near Three Gorges, the finite element analysis by using ABAQUS software was used to simulate three different types of advanced support of left side of the tunnel portal excavations in the strongly to completely weathered granite rock mass, namely, no advance support, doublelayer small diameter perforated pilot grouting pipe and large diameter perforating pilot grouting pipe shield. The results show that, in the process of Three Benches excavation, the large diameter perforated pilot grouting pipe shield method had obvious effect in controlling the excessive settlement deformation and development of plastic zone expansion, the predicted settlement deformation characteristics and cumulative value are close to the measured value, while the doublelayer small diameter perforated pilot grouting pipe method had little effect on controlling the deformation and overall failure of the surrounding rock mass. Therefore, the selecting of the advanced support type of large diameter perforated pilot grouting pipe shield method for the left tunnel portal of Zhaizibao Tunnel exit was validated. This project provides a method the design and construction of the advance support for the similar tunnel in the future.

Key words: tunnel in mountain, shallow buried, advance support, settlement and deformation