Mechanisms of accelerated flow of sediment by rollers of air bubbles in soil

2023 Fiscal Year Final Research Report

• Project/Area Number: 21K18741
• Research Category: Grant-in-Aid for Challenging Research (Exploratory)
• Allocation Type: Multi-year Fund
• Review Section: Medium-sized Section 22:Civil engineering and related fields
• Research Institution: Utsunomiya University
• Principal Investigator: UNNO TOSHIYASU 宇都宮大学, 地域デザイン科学部, 准教授 (50570412)
• Co-Investigator(Kenkyū-buntansha): 加村 晃良 東北大学, 工学研究科, 准教授 (80761387) ; 菊本 統 横浜国立大学, 大学院都市イノベーション研究院, 教授 (90508342)
• Project Period (FY): 2021-07-09 – 2024-03-31
• Keywords: 不飽和土 / 間隙水 / 間隙空気 / サクション / 繰返し載荷 / 液状化 / 三次元個別要素法 / ベアリング効果

Outline of Final Research Achievements

In recent years, ground disasters involving soil turning into mud and flowing during natural calamities like earthquakes and heavy rains have become increasingly frequent. This phenomenon, where large quantities of soil travel over long distances, remains poorly understood. Our study hypothesizes that air bubbles trapped within collapsing soil significantly reduce its strength and stiffness, leading to fluid-like behavior. To confirm this, we conducted mechanical tests and numerical analyses to investigate the impact of pore air on soil's shearing behavior. We created synthetic soil samples by introducing bubbles using special chemical agents. The experiments revealed that soil containing many bubbles in its pores exhibited shear softening behavior, even in conditions not typically associated with softening. These findings highlight the role of pore air in soil's susceptibility to fluidization and offer new insights into ground failure mechanisms during natural disasters.

Free Research Field

地盤工学

Academic Significance and Societal Importance of the Research Achievements

自然災害により表層地盤が泥状になり崩壊する流動性崩壊が多発している．この崩壊部は，地下水位より上の比較的浅い不飽和土層である．本研究では，地震動等の外力を受け軟化する不飽和土の力学挙動を室内要素試験，数値解析を用いて検討し，不飽和土の軟弱化メカニズムの把握を試みている．
その結果，従来，間隙空気により高いせん断強度や液状化抵抗を有するとされる不飽和土でも，土中の間隙空気と間隙水の状態によっては十分な強度を発揮しない状態に至ることを明らかにした．この事実は，不飽和土の力学挙動に対し間隙空気と間隙水の状態を精緻に把握する重要性を示す結果であるとともに，不飽和土の耐震検討に対して有益な知見を与える．