Liquefaction potential of pumice sand fill subjected to suffusion: are fine particles are good or bad?

2023 Fiscal Year Final Research Report

• Project/Area Number: 21H01421
• Research Category: Grant-in-Aid for Scientific Research (B)
• Allocation Type: Single-year Grants
• Section: 一般
• Review Section: Basic Section 22030:Geotechnical engineering-related
• Research Institution: Hokkaido University
• Principal Investigator: Watabe Yoichi 北海道大学, 工学研究院, 教授 (00371758)
• Co-Investigator(Kenkyū-buntansha): 佐々 真志 国立研究開発法人海上・港湾・航空技術研究所, 港湾空港技術研究所, グループ長 (10392979) ; 椋木 俊文 熊本大学, 大学院先端科学研究部(工), 教授 (30423651)
• Project Period (FY): 2021-04-01 – 2024-03-31
• Keywords: 細粒分含有率 / 内部侵食 / せん断強さ / 液状化強度 / 火山灰質砂 / 締固め / 骨格構造

Outline of Final Research Achievements

In this study, using volcanic ash sands with adjusted three fine particle contents, soil specimens were prepared by compaction at different degree of compaction and water content. Consolidated undrained triaxial tests and cyclic loading undrained triaxial tests were conducted with and without internal erosion. The relationship between the occurrence of internal erosion, changes in undrained shear strength, and changes in liquefaction strength were discussed in association with the skeletal structure formed during compaction, especially the macroporosity formed under dry-side compaction conditions. As a result, it was confirmed that if the soil skeleton, which is mainly formed with coarse particles, remains intact even when the fine particles are migrated, their strength tends to increase due to internal erosion.

Free Research Field

地盤工学

Academic Significance and Societal Importance of the Research Achievements

2018年北海道胆振東部地震で液状化被害を受けた札幌市里塚地区は，1970年代に切土・盛土によって造成された．この地区の盛土材は3～4万年前の支笏火山噴火に伴う火砕流堆積物であり，当時の土地造成では締固めが十分に行われていない緩詰め状態であったことがわかっている．施工管理がしっかりなされれば，同様の液状化被害は防げるものと考えられる．しかし，造成直後に発生する細粒分の流出（サフュージョンと称する内部侵食）が多少なりとも発生することは避けられない．本研究から得られた非排水せん断強さや液状化強度に与える細粒分含有率およびその変化の影響は，今後の盛土の品質管理の上で役立つ重要な知見となる．