| Rock tunnels are generally strong structures against earthquakes compared to other structures on the ground surface. However, collapse of permanent lining occurred in recent worst earthquakes in Japan such as 2024 Noto Peninsula earthquake and 2016 Kumamoto earthquake. Reviewing tunnel damage in recent large earthquakes, the authors noted that the ground supported by tunnel supports was spared from collapsing in almost all cases, even though the permanent lining collapsed. This suggested that the safety of tunnel users can be ensured by preventing the permanent lining from falling, even if the lining failed. In this paper, the authors suggest that rebar has the potential to fail-safe function for cast-in-place permanent lining against collapse during large earthquakes. To verify the effectiveness, full-scale lining loading tests and laboratory tests were performed and calculation result for confirming the effect was discussed. Major conclusions include: a single bar reinforcement has a potential to hold the weight of the permanent lining according to the calculation. The effect was also confirmed by the laboratory elemental experiments up to a shear displacement of at least 10 cm. In addition, even if the permanent lining was failed by external force and shifted by more than 10 cm, the rebar did not break and the whole lining remained united in the full-scale loading test. |
