Mechanism of river embankment collapse by overflow of river and water seepage

2018 Fiscal Year Final Research Report

• Project/Area Number: 16K06519
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Research Field: Hydraulic engineering
• Research Institution: Waseda University
• Principal Investigator: Sekine Masato 早稲田大学, 理工学術院, 教授 (60187854)
• Project Period (FY): 2016-04-01 – 2019-03-31
• Keywords: 河川工学 / 水工水理学 / 移動床水理学 / 河川堤防の決壊 / 粘着性土の浸食 / 洪水

Outline of Final Research Achievements

It was clarified experimentally that a noticeable difference appeared in the process of collapse according to the ratio of "gravel, sand, clay" constituting the embankment, and the elucidation of the mechanism was revealed considerably. When clay is contained enough to fill the gap of the gravel, erosion is suppressed because of the erosion resistance of clay, and the embankment becomes much more tenacious and difficult to collapse. In addition to clay and sand, when gravel is contained in a certain ratio, the effect of the interlocking between the gravel particles becomes noticeable, and the embankment collapse is difficult to cause. If clay is contained more than a certain ratio, the embankment becomes easier to deform. If the content ratio of the gravel is too large, the permeability of the entire material is increased and collapse by penetration. It is believed that the best ratio of mixture among "gravel, sand, and clay" exists for a tenacious embankment.

Free Research Field

河川工学、水工水理学

Academic Significance and Societal Importance of the Research Achievements

地球規模での気候変動と気象の極端化の影響により，記録的な豪雨が毎年のように発生しています．これに伴い，河川での堤防決壊も稀ではなく，2015年の鬼怒川の決壊に伴う大規模浸水を始め，国内のどこかで毎年のように甚大な被害に遭遇するようになりました．河川堤防は洪水による被害を食い止める最後の砦であるため，堤防を決壊し難い「粘り強い」ものとしていく必要があります．本研究によれば，堤防材料に占める「礫・砂・粘土」の比率に最適値が存在することが示され，現時点で言えば「3 : 4 : 3」がこれに当たるとの結論が得られました．これは，これまでに経験的に定めてきた指標に力学的な裏づけを与える結果と言えます．