Development of face stability theory considering progressive failure due to tunnel excavation

2023 Fiscal Year Final Research Report

• Project/Area Number: 21K14238
• Research Category: Grant-in-Aid for Early-Career Scientists
• Allocation Type: Multi-year Fund
• Review Section: Basic Section 22030:Geotechnical engineering-related
• Research Institution: Saitama University
• Principal Investigator: Togashi Yota 埼玉大学, 理工学研究科, 助教 (90753294)
• Project Period (FY): 2021-04-01 – 2024-03-31
• Keywords: トンネル / 切羽土圧 / シールド / 極限釣合い / 土圧理論

Outline of Final Research Achievements

This study proposes a theory for estimating tunnel face pressure that uses a curved slip line and takes into account loosening earth pressure. The following findings were obtained through this study.
1. It is confirmed that the proposed theory can properly evaluate the face pressure by taking into account the nature of the ground as frictional material. It is shown that the slope of the slip line has little influence on the face pressure characteristics, but the face pressure increases when the failure zone width is large.
2. Tunnel pulling experiments were conducted to simulate the stress release associated with tunnel excavation, and LiDAR and PIV analysis were used to obtain detailed information on the shape of the failure zone. As a result, it was found that a failure zone is locally generated as frictional resistance increases due to soil cover and other factors. Differential equations that can describe this phenomenon were also constructed.

Free Research Field

トンネル

Academic Significance and Societal Importance of the Research Achievements

切羽土圧の推定は非常に複雑な問題であり，トンネル技術が飛躍的に進んだ今日においても極めて重要な技術課題である。現在までで切羽土圧の推定で最も有力な方法は，鉛直なすべり線を想定したSiloの計算より地山の摩擦抵抗による鉛直土圧を考慮した上で切羽直前のくさびの釣合いを解くことで切羽土圧を得る方法だが，すべり線の形状が現実には直線とは言えない場面が多い。提案理論は未だ改良の余地があるが，既往方法よりも正確に切羽土圧を推定できる可能性を秘めており，建設実務に直結できる社会的意義の大きい成果と考えている。