Design and construction of enlarging shield tunnel sections of large dimensional shield tunnels for the non-open-cut method

The use of the enlarging method for large dimensional shield tunnel construction is essential in the building of branch connections and ramps, particularly when constructing underground roads in narrow urban areas. In this paper, the non-open-cut method, which excavates underground, used in The Central Circular Shinjuku Route of Tokyo Metropolitan Expressway is reported. This paper describes the construction of the cut and open of a part of steel segments installed in two parallel large dimensional shield tunnels over a total length of 100 m using the non-open-cut method. The pipe roofing method was adopted for three reasons: the excavation depth is relatively shallow; the location is just beneath a trunk road intersection; and important utilities are laid underground at various locations. And, new construction methods such as use of pre-strutting, which involves the placement of preceding struts using pipe-jacking in order to stabilize the tunnels and to prevent deformation, as well as preloading to reduce settlement of roof pipes are employed. Furthermore, in order to ensure safety during the construction work and to reduce adverse environmental effects such as ground settlement, various types of behavior prediction analysis have been carried out and monitoring-feed backing to construction are performed as construction continues. (A) This paper was presented at Safety in the underground space - Proceedings of the ITA-AITES 2006 World Tunnel Congress and the 32nd ITA General Assembly, Seoul, Korea, 22-27 April 2006. For the covering abstract see ITRD E129148. “Reprinted with permission from Elsevier”.