Abstract: The construction of a municipal tunnel that intersecting with a rail transit tunnel might adversely affect the structural integrity of the transit tunnel. An effective method to reduce the safety hazards of the transit tunnel is to appropriately determine the construction sequences of the tunnels. This paper presents the case history of the construction of Chengdu Metro No. 4 Line tunnel which was intersect the municipal tunnel under the Wenquan Boulevard. The consequence was to excavate the transit tunnel using the shielded method and the open cut construction method to install the municipal tunnel above. During the construction of upper protective isolation layer of the transit tunnel, the bottom slab of the municipal tunnel and the uplift piles, the posttensioned ground anchors were installed in between the uplift piles. The transit tunnel could be shielded tunneling can be excavated after the adjacent soil mass was stabled. The prestresses could then be released progressively. During this period, the tunnel frame structures and the underground space structures could be installed. The finite element analysis conclude that this design scheme was appropriate. The prestress in the uplift piles could effectively reduce the structure safety hazards within the shielded zone.

Key words: Municipal Tunnel, Rail transit, Underground Space Development, Protective Isolation Layer, Pre-Stressing