Elucidation of deformation and failure mechanism of unsaturated soil subjected to cyclic water absorption and drainage history

2022 Fiscal Year Final Research Report

• Project/Area Number: 20K14821
• Research Category: Grant-in-Aid for Early-Career Scientists
• Allocation Type: Multi-year Fund
• Review Section: Basic Section 22030:Geotechnical engineering-related
• Research Institution: Nagoya University
• Principal Investigator: Yoshikawa Takahiro 名古屋大学, 工学研究科, 助教 (20771075)
• Project Period (FY): 2020-04-01 – 2023-03-31
• Keywords: 不飽和土 / 弾塑性 / 慣性力 / 吸水破壊 / 降雨

Outline of Final Research Achievements

To elucidate the collapse mechanism of natural slopes and embankments due to rainfall, we first conducted triaxial compression tests where unsaturated soil specimens deformed to fail due to water absorption and their numerical simulations. As a result, it was found that if the initial stress ratio of the specimen is not extremely high, after the suction decreases to zero, the stress ratio and saturation degree increase further due to water absorption caused by the increase in pore pressure, eventually leading to failure by the "softening behavior with plastic volume expansion" exhibited above the critical state line q=Mp'. Next, reproduction analyses of rainfall model experiments and the Atami embankment collapse showed that rainfall infiltration and groundwater inflow caused the same deformation and failure mechanism as in the case of the specimens described above, leading to eventual slip failure of the model slope and the Atami embankment.

Free Research Field

地盤工学

Academic Significance and Societal Importance of the Research Achievements

これまで降雨による自然斜面や盛土の崩壊要因として、不飽和土の飽和化や間隙圧上昇による強度低下等が挙げられていたが、申請者らが開発した飽和・不飽和両対応の慣性力考慮の弾塑性有限変形解析コードを用いて、限界状態線q=Mp’の上側で示す「塑性体積膨張を伴う軟化挙動」を呈して、土供試体、模型斜面および実被災盛土が吸水により変形から破壊に至ると具体的に示すことができた。今後、崩壊メカニズムに基づく対策工の評価・提案を行っていく上でも、意義のある研究成果となった。