Occurrence and motion mechanism of long runout landslide due to rainfall and earthquake in tephra deposit slope

2022 Fiscal Year Final Research Report

• Project/Area Number: 19H01980
• Research Category: Grant-in-Aid for Scientific Research (B)
• Allocation Type: Single-year Grants
• Section: 一般
• Review Section: Basic Section 17030:Human geosciences-related
• Research Institution: Shimane University
• Principal Investigator: Wang Fawu 島根大学, その他部局等, 名誉教授 (10324097)
• Co-Investigator(Kenkyū-buntansha): 中川 光弘 北海道大学, 理学研究院, 特任教授 (50217684) ; 志比 利秀 島根大学, 学術研究院環境システム科学系, 助教 (60311792) ; 宮島 昌克 金沢大学, 地球社会基盤学系, 教授 (70143881) ; Andreas Auer 島根大学, 学術研究院環境システム科学系, 講師 (80778613)
• Project Period (FY): 2019-04-01 – 2022-03-31
• Keywords: 斜面防災 / 地すべり / 高速長距離 / 火砕物 / 風化 / 粒子破砕 / 非排水せん断 / 粘土鉱物

Outline of Final Research Achievements

This project studies the initiation and motion mechanism of rapid and long runout landslides generated in clusters caused by Iburi earthquakes. In this study, we conducted a detailed field survey to elucidate the topography, geology, and groundwater conditions where landslides occurred, and to understand the characteristics of the long-distance motion of the landslides. We also used GIS methods to analyze many influence factors that contributed to the occurrence of landslides. Most importantly, long-term field observations have revealed that the soil in the Ta-d layer, which is the sliding zone, has an extremely high void ratio, extremely weak shear resistance, and high degree of saturation regardless of rainfall. Furthermore, the existence of halloysite, which is the fundamental reason of its high water retention and water absorption, was confirmed, and it make the study useful for landslide disaster prevention.

Free Research Field

斜面防災

Academic Significance and Societal Importance of the Research Achievements

学術的意義：降下火砕物Ta-d層が風化作用によって、ハロイサイトが形成され、高い間隙比、低いせん断抵抗、季節的降雨と関係なく、地下水面以上でも高い飽和度を持つことで、地震によって、すべりゾーン液状化現象が発生することで、群発的高速長距離運動地すべりの原因として見出された。
社会的意義：従来の排水工法が効かなくて、ハロイサイトを排除すれば、高速長距離運動地すべりを根本的に対処できることを意味しており、今後の斜面防災に資することとなった。