Optimal Analysis of Excavation Method of a Shallow Tunnel Beneath Expressway

By using the three-dimensional numerical modeling, the different excavation processes of a shallow tunnel with cover to depth ratio of less than 1 were modeled. The key parameters such as settlements of crown and ground surface, displacements of lining and the stress changing during the threedimensional excavation processes were compared and analyzed.Resultsshow that although the excavation area of each excavation step is relatively small when using the double-side-drift method, the controlling effect of which on the ground and crown settlements is far from satisfied due to its complex excavation process and late closing time of the primary lining. Compared with the double-side-drift method, the central-diaphragm-wall method is better in effectively controlling the settlements of crown and ground surface, which is especially true for the central-cross-diaphragm-wall method due to the strengthen effect of the temporary inverts. The optimal analysis before excavation is very important in choosing appropriate excavation method to insure finishing the tunnel construction in time.