2022 Volume 10 Issue 1 Pages 82-95
The 2019 typhoon No. 19 hit Japan on October 12. It caused severe damage to Kanto-koshin and Tohoku areas upon landing. The authors conducted damage investigations on all the breached sections of river dikes in Ibaraki prefecture in total five times after the disaster occurred. The survey results showed that: 1) the breach of river dikes in Ibaraki prefecture might be attributed to the erosion of levee slopes caused by the overflow; 2) no signs of soil ejection and piping were found around the breached sections of river dikes; 3) some river dikes with the crest pavements and revetment blocks for both side surfaces demonstrated that they could occasionally be collapsed by the overflow.
At the time of the above-mentioned survey, geomaterials were retrieved from both slope surfaces of each undamaged dike section, which was adjacent to the damaged area, for laboratory tests. The test results revealed that most of the retrieved materials were non-/low-plastic sandy or gravelly soils with fines content less than 20%.
