Seismic assessment of Nagoya Port Island against Nankai Trough earthquake

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Abstract

In order to maintain the function of Nagoya Port, 1.3 million m3 soil must be dredged every year which is currently filled at Nagoya Port Island (hereinafter, PI) as a temporary disposal area. However, the initial envisioned capacity of the PIs to accept dredged soil has already been exceeded, even though the temporary banks built on top of the reclaimed ground have increased their capacities. Therefore, should a megathrust earthquake occur, it is likely that, in addition to damaging the revetment and temporary banks, the earthquake would cause large volumes of high-piled dredged soil to flow into the harbor, where it could block ship channels. This would not only reduce the functionality of Nagoya Port, it would also lead directly to delays in disaster relief and recovery/reconstruction support. For this reason, seismic assessment of the PIs and improvements to their earthquake resistance are urgent issues. In this study, we used a computer simulation to reproduce a PI in its current state, while taking into consideration its actual construction history, in order to gain an understanding of the damage that would occur during and after the largest envisioned Nankai Trough earthquake. Furthermore, the model used predicted how earthquake damage would progress if dredged soil were to continue to be added onto the PI without restriction. The main conclusions are as follows. 1) If the current situation remains unchanged, a certain amount of deformation would occur on the PI as a result of the earthquake, but the damage extent would not be such that dredged soil would flow into the harbor. 2) On the other hand, if the existing height were raised by 4 m, it would be impossible to prevent the lateral displacement of dredged soil, and there would be a high risk of dredged soil flowing into the harbor. These results indicate that continuing to raise the height of the reclaimed land is dangerous in terms of PI earthquake resistance. The analysis code used in this paper is the soil–water coupled finite deformation analysis code GEOASIA.

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