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

摘要

The use of the enlarging large dimensional shield tunnel construction method is essential in the building of branch connections and ramps, particularly when constructing underground roads in narrow urban areas. The Central Circular Shinj-uku Route of Tokyo Metropolitan Expressway is now under construction using both the open-cut method, which excavates from the ground surface, and the non-open-cut method, which excavates underground. In this paper, the non-open-cut method is reported. This paper describes the construction of the cut and open of a part of steel segments installed in two 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 large road intersection; and important underground utilities are laid underground at various locations. With this application, 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 two and three-dimensional sequential FEM analyses have been performed, and to reduce adverse environmental effects, such as ground settlement, two-dimensional FEM analysis have been carried out. And attaching various sensors with shield segments and timbers, monitoring-feed backing system to construction are set up as construction continues.