Abstract
Constructions of twin type closed tunnel with a center pillar, which stands very close to each other, tend to increase because of the limitation of the land utilization. This paper deals with the approach of the design method of the twin type closed tunnel which does not construct this center pillar. The authors had an experience with the construction of three types of twin closed tunnels on the same tunneling site. By this experience, the ordinary closed tunnels have some safety and environmental problems concern with the construction of center pillars. An applicability study of this construction method is described by comparison between the results of numerical analysis and the field measurements at this construction.
