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二次元流況解析による四万十川里川沈下橋の流失原因とその対策法に関する考察

田内 敬祐^*1, 岡田 将治^*2, 張 浩^*3

^*1国土交通省四国地方整備局大洲河川国道事務所　〒795-8512 愛媛県大洲市中村210
^*2高知工業高等専門学校ソーシャルデザイン工学科　〒783-8508 高知県南国市物部乙200-1
^*3高知大学理工学部地球環境防災学科　〒780-8520 高知県高知市曙町2丁目5-1

Investigation of the Failure Mechanisms of the Satokawa Low-Water Bridge in the Shimanto River during the Flood and its Countermeasures by using two-dimensional flow analysis

Keisuke TAUCHI^*1, Shoji OKADA^*2 and Hao ZHANG^*3

^*1Ministry of Land, Infrastructure, Transport and Tourism, Shikoku Regional Development Bureau
^*2National Institute of Technology, Kochi College
^*3Kochi University

Abstract

The Satokawa low-water bridge in the Shimanto River has been washed away four times in the past and restored each time. However, its main cause of failure has not been clarified. Therefore, we clarified the hydrological cause of the washed away of the Satokawa low-water bridge and examined more effective countermeasures. Firstly, we selected the Jogu low-water bridge where has the similar specification as Satokawa low-water bridge and has no experience of washed away in the past to compare with the Satokawa low-water bridge. Then we conducted the two-dimensional flow analysis and hydraulic experiments of Satokawa section and Jogu section to clarify the flow characteristics. From these results, we revealed that the main cause of washed away of the Satokawa low-bridge was upward flow near slab and rocky area of left bank, and showed countermeasures.

Key Words: Low-water bridge, washed away, two-dimensional flow analysis, Shimanto River