양산단층대 지역에서 터널굴착 중 붕락 메카니즘에 대한 연구

Abstract

Tunnels are commonly constructed at depth by taking into account the characteristics and properties of the ground, Due to the non-homogeneous nature of the ground, it is difficult to estimate the behavior of tunnel accurately. Thus, the ground characteristic should be analyzed during site investigation and the results should be incorporated during design process.

However, the present site investigation technique has some limitations to analyze the ground characteristic clearly. The real condition of the ground may differ from what is anticipated because there is always some level of uncertainty when attempting to anticipate ground characteristics, especially the target tunnels selected in this study.

These tunnels are located in very weak ground such as the faulted zones(faults in unconsolidated sediments). The tunnels in this study have been collapsing often during construction because the ground behavior anticipated in design process is completely different to that of the actual site.

In this study, four tunnel collapse cases which occurred in the Yangsan fault zone were analyzed. Two collapse cases were related to a partial ceiling fall at the same time of face excavation. The other two cases were related to the collapse of a tunnel near the entrance. After the excavation had been completed and a certain amount of time elapsed, only then did the progressive failure occur.

During tunnel construction process, the next step in the excavation process of the tunnel face starts after the displacement convergence of the excavated face. Thus, the collapse of the tunnel near the starting point was unusual compared to a typical tunnel failure, which happens at the same time of face excavation. Such a progressive failure may be related to the ground condition of the tunnel construction site located in the faulted zones.

In addition, the mechanism of tunnel failure observed in the Yangsan fault zone is closely related to ground water which may cause a small size failure, followed by a second larger failure. Thus, rapid reinforcement work is necessary after the first collapse with applying preloading for tunnel stability.