SOIL PROPERTIES OF RIVER DIKES IN IBARAKI PREFECTURE COLLAPSED BY THE 2019 TYPHOON NO. 19

Abstract

 The 2019 typhoon No. 19 hit Japan on October 12. Severe damage to Kanto-koshin and Tohoku areas was brought due to its landing. The authors conducted damage investigations for all the breached sections of river dikes in Ibaraki prefecture in total five times after the disaster has occurred. The survey results showed that: 1) the breach of river dikes in Ibaraki prefecture may have been attributed to erosion of dike slope caused by the overflow; 2) the signs of soil ejection and piping were not 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 the 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%.