Abstract: The tunnel between Zaoshan station and Licun station of Qingdao metro line 2 is constructed under the Licun-river. The top of the tunnel which is located in the strongly weathered granite layer is covered by sand layer of high permeability and silt clay layer of impermeability. The construction safety must be ensured so that it would not destroy the upper natural aquifer. Five schemes of construction were put forward based on the geological conditions and construction experience. The tunnel excavation process was numerically simulated. Almost all of the factors that influence the deformation and the development of plastic zone of the surrounding rock were taken into account, including construction speed, excavation step distance, excavation method and supporting structures. The most suitable construction scheme was selected by analyzing the deformation regularity of the surrounding rock and comparing the curves of deformation at key locations and settlement at the top of the tunnel in each scheme. Furthermore, the construction parameters of the optimal scheme were secondly optimized according to the control indexes of the range of plastic zone of overlying rock, the settlement of the top and the convergence value of the sides. In the precondition of ensuring the water resisting effect of silt clay layer, the construction speed was greatly increased. Moreover, the construction method provides scientific basis and technical guidance for safe and rapid construction.

Key words: Qingdao Metro, river-crossing tunnel, water-resisting layer, construction optimization