Elucidating the deformation of bedrock caused by hydromechanical processes

2023 Fiscal Year Final Research Report

• Project/Area Number: 21H01593
• Research Category: Grant-in-Aid for Scientific Research (B)
• Allocation Type: Single-year Grants
• Section: 一般
• Review Section: Basic Section 25030:Disaster prevention engineering-related
• Research Institution: Shimane University
• Principal Investigator: Kogure Tetsuya 島根大学, 学術研究院環境システム科学系, 准教授 (70534006)
• Co-Investigator(Kenkyū-buntansha): 土井 一生 京都大学, 防災研究所, 准教授 (00572976) ; 小松 満 岡山大学, 環境生命自然科学学域, 教授 (50325081)
• Project Period (FY): 2021-04-01 – 2024-03-31
• Keywords: 地下水挙動 / ひずみ変化 / 斜面安定性 / 深層崩壊 / 割れ目

Outline of Final Research Achievements

This study investigated the relation between groundwater migration and bedrock deformation with drilling a 50 m-deep borehole to understand the occurrence mechanisms of deep-seated landslides which could be induced by extremely intense rainfall. Distributed fiber optic sensing, which detect the changes in temperature and strain, was adopted for the monitoring of water migration and bedrock deformation: spatial resolution along the borehole was 5 cm. Changes in temperature and strain obtained by cables allow us to understand water migration and bedrock deformation, respectively. Active-heating method, in which a metallic wire in a cable is heated, revealed water level because it shows a temperature distribution along the borehole, where the degree of temperature increase is lower around water due to thermal absorption by water. The depths of strain accumulation almost coincident with water depths, indicating groundwater migration through cracks might induce bedrock deformation.

Free Research Field

自然災害科学，地形学，応用地質学

Academic Significance and Societal Importance of the Research Achievements

近年，地球温暖化に伴い短時間で非常に強い降雨現象が増えている。そうした降雨により通常の斜面崩壊より規模が大きい深層崩壊が発生する可能性が高まる。本研究では，深層崩壊が発生する地下数十メールの深さでは日常的にどのような現象や変化が起きているか調べるため，深層崩壊の原因となる地下水の動きと地盤変形との関係を調べた。その結果，地下水の動きが活発な場所（恐らく岩盤の割れ目が多い場所）で地盤変形が生じやすいことを確認した。この成果は，地下水が流動しやすい場所をボーリング孔掘削により把握することで，将来の深層崩壊発生リスクすなわち斜面安定性を評価できる可能性を示す。