ABSTRACT
For example, several shallow overburden tunnels were excavated in unconsolidated ground during the construction of a new expanding bullet train line in Japan. In these construction sites, ground subsidence often occurred due to the low stiffness of the unconsolidated ground and a significant reduction in the arching effect due to the shallow overburden (Iura et al., 2009). In the above-mentioned construction sites, the same settlements of the ground surface, the crown, and the foot of the tunnel occurred, as shown in Figure 1
1 INTRODUCTION
1.1 Excavation of shallow overburden tunnel
Almost 40 years ago, NATM were introduced in Japan. Currently, it becomes the standard tunnel construction method in Japan. NATM effectively uses the ground arch action with shotcretes and rock bolts. In order to clarify the mechanical behavior of excavated ground and the role of both the shotcrete and the rock bolt, several discussions of field measurements and numerical works have been conducted. Since not only finite element method but also various numerical methods have been progressed, the mechanical behavior of excavated ground and the support mechanism of the shotcrete and the rock bolt could be estimated. Consequently, NATM could be effectively applied to tough geological conditions in Japan and it has been grown up as a Japanese taste NATM.
