Study on the behavior of an ultra-large section tunnel project in unconsolidated ground-design and construction of the Minoh toll road tunnel

This paper discusses the Minoh tunnel construction. The geology at its south portal is unconsolidated soil, with a high groundwater level. A significant amount of water inflow was therefore anticipated. In such adverse ground, this tunnel with a maximum excavation section of 313 m 2, which is one of the largest sections in Japan, was successively constructed using the side-drift advance method with various new techniques. During tunneling, informatics technologies were fully utilized, by feeding back various measurement results to design and construction, thereby enabling selection of suitable auxiliary stabilizing techniques and excavation methods. The auxiliary methods involved were pipe roof (812.8 mm in diameter, 90 m long), long steel pipe forepiling, and long face bolts. In addition, "quasi-high fluidity concrete" was used to place high quality lining.