Stability analysis and excavation schemes of large-span highway tunnel under complex geological conditions

More and more practice problems arise during the construction of the big-span highway tunnels due to the complexity of the geological conditions, such as geological disasters, failure of the shot and lining concrete, etc. Tunneling excavation is actually the process of stress redistribution and rock deformation, which are much influenced by different construction methods and sequences. A case study of the east Mao Mountain tunnel on the Ning-Chang highway, China, is carried out in this paper. The three dimensional numerical simulation is conducted on different excavation schemes in the condition of pre-designing support system using the FLAC ID software. The displacement behavior and stress characteristics are analyzed to propose the reasonable tunneling scheme. Accordingly, the stability of selected scheme is predicted. Moreover, the simulation results are compared with field monitoring data. The pre-designing support parameters of the large-span highway tunnel are evaluated. The results of this study are expected to be useful for the successive design and construction control.