The NATM(New Austrian Tunnelling Method) has been used for tunnelling since 1980"s in Korea. But Collapses of tunnel under construction take place frequently, especially at urban areas. This paper represents the study and analysis on the reinforcement method of tunnel under construction in Korea. In this study, ground inspection, geological investigation, laboratory test and numerical analysis by means of finite difference method were carried out. The tunnel excavation was stopped because of over excessive brake of tunnel crown and shotcrete was installed to prevent deformation of adjacent ground as the temporary method. From the result of field survey and geological investigation, it is found that the soft weathered soil was distributed to the ground of tunnel invert unlike first investigation. The results of the analysis and the study show that the SGR(Space Grouting Rocket) method and umbrella arch method can be applied for the stability of tunnel excavation and in addition the reinforcement of concrete lining is required for long-term stability of tunnel.
The tunnel is constructed to fulfil Korea's transportation requirement as a subway tunnel. The NATM was adopted as tunnelling method. The depth from the ground surface to the top of tunnel is about 13 meters. And the tunnel was excavated after polyurethane grouting at the crown part of tunnel. The support pattern of tunnel is summarized in table 1. The site investigation was carried out during the excavation of tunnel. As a result, it is found that the initial tunnel design was based on wrong data obtained from the initial ground investigation below surface level. Namely, from the initial ground investigation the adjacent ground around tunnel was classified to weathered rock or soft rock, but investigation during the construction revealed that weathered soil was distributed to the depth of tunnel invert level.
