Abstract: The tunnel section in the emergency stopping zone in a threelane Qingfeng Tunnel of KummingChuxiong Expressway has large size and a flat oblong cross section. Both advantages and disadvantages of two different tunnel excavation sequences, ThreeBench Method and Temporary CentralWall Method, were evaluated and the threebench excavation method was selected for the tunnel excavation. The entire process of the constructionsequence was numerically simulated, and the selected construction sequence was feasible and safe. The analytical results, such as, deformation in the tunnel, stress in the supporting structures and the plastic zones in the rock mass, were compared with the construction monitoring results. The results indicated that the stress in both the rock mass and steel arch supporting structures were small and the construction sequence was safe.

Key words: large-span flat tunnel, construction mechanics, 3D numerical simulation, field monitoring