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Study on the generation mechanism of landslides in terms of the weathering zones of rocks

Research Project

Project/Area Number 11680469
Research Category

Grant-in-Aid for Scientific Research (C)

Allocation TypeSingle-year Grants
Section一般
Research Field Natural disaster science
Research InstitutionKyoto University

Principal Investigator

CHIGIRA Masahiro  Kyoto University, Disaster Prevention Research Institute, Professor, 防災研究所, 教授 (00293960)

Project Period (FY) 1999 – 2001
Project Status Completed (Fiscal Year 2001)
Budget Amount *help
¥2,300,000 (Direct Cost: ¥2,300,000)
Fiscal Year 2001: ¥500,000 (Direct Cost: ¥500,000)
Fiscal Year 2000: ¥500,000 (Direct Cost: ¥500,000)
Fiscal Year 1999: ¥1,300,000 (Direct Cost: ¥1,300,000)
KeywordsWeathering / Landslide / Granite / Ignimbrite / Tuff / Sedimentaryu rocks / Rainfall / Infiltratoin / 気相晶出作用 / シラス / マサ / 泥岩 / 砂岩
Research Abstract

To clarify the generation mechanism of shallow landslides, I studied the weathering profiles, their formative mechanisms, and the relationships between the profiles and landslide generation for granitic rocks, ignimbrite, and sedimentary rocks. The major results are as followings :
1) As major weathering processes of granitic rocks, micro-sheeting and spheroidal weathering were recognized. Granitic rocks, which are micro-sheeted by unloading, are loosened intensively to a depth of a few meters with a well defined front. This loosened zone increases its thickness and finally slides. Spheroical weathering proceeds by micro-cracking and chemical leaching. Moderately weathered granite, which are made through geological time, is loosened rapidly to a depth of a few meters when it is exposed by artificial cutting or natural denudation ; rainwater infiltrates through this loosened zone preferentially. The saturation, generation of pore pressure, and the decrease of cohesion by the loss of suct … More ion of this loosened material become the basic factors for the generation of landslide.
2) Ignimbrite varies from unwelded to strongly welded tuff. Unwelded ignimbrite is weathered to have a well-defined front, which acts as a capillary barrier between the fresh permeable tuff and the overlying less permeable weathered tuff. Infiltrating rainwater increases the weight of the weathered tuff and decreases its cohesion because of suction disappearance. These are the basic factors of the landslide of unwelded ignimbrite.
3) Vapor-phase crystallized ignimbrite has a well defined weathering front between the fresh or hydrated impermeable tuff and the overlying strongly weathered, permeable tuff. The weathered tuff on the front is exfoliated parallel to slope surface by the intensive chmical leaching. The saturation, generation of pore pressure, and the decrease of cohesion by the loss of suction of this weathered tuff become the basic factors for the generation of landslide.
4) Sedimentary rocks generally have oxidation and dissolution fronts, which are made by the sequential reaction between the rocks and the infiltrating water. This weathering process and the resultant change of mechanical properties are the major causes of the common type of landslide of sedimentary rocks, which have slip surfaces along or below the oxidation front. Less

Report

(4 results)
  • 2001 Annual Research Report   Final Research Report Summary
  • 2000 Annual Research Report
  • 1999 Annual Research Report
  • Research Products

    (27 results)

All Other

All Publications (27 results)

  • [Publications] Chigira, M., Nakamoto, M., Nakata, E.: "Weathering mechanisms and their effects on the landsliding of ignimbrite subject to vapor-phase crystallization in the Shirakawa pyroclastic flow, northern Japan"Engineering Geology. (In press).

    • Description
      「研究成果報告書概要(和文)」より
    • Related Report
      2001 Final Research Report Summary
  • [Publications] Chigira, M.: "Geologic factors contributing to landslide generation in a pyroclastic area : August 1998 Nishigo Village, Japan"Geomorphology. (In press).

    • Description
      「研究成果報告書概要(和文)」より
    • Related Report
      2001 Final Research Report Summary
  • [Publications] Chigira, M., Inokuchi, T.: "Landslides triggered by August 1998 intense rainfall, northern Japan"Landslide News. (In press).

    • Description
      「研究成果報告書概要(和文)」より
    • Related Report
      2001 Final Research Report Summary
  • [Publications] Chigira, M.: "Micro-sheeting of granite and its relationship with landsliding specifically after the heavy rainstorm in June 1999, Hiroshima Prefecture, Japan"Engineering Geology. 59. 219-231 (2001)

    • Description
      「研究成果報告書概要(和文)」より
    • Related Report
      2001 Final Research Report Summary
  • [Publications] Chigira, M., Oyama, T.: "Mechanism and effect of chemical weathering of soft sedimentary rocks"Engineering Geology. 55. 3-14 (1999)

    • Description
      「研究成果報告書概要(和文)」より
    • Related Report
      2001 Final Research Report Summary
  • [Publications] Oyama, T., Chigira, M.: "Weathering rate of mudstone and tuff on old unlined tunnel walls"Engineering Geology. 56. 15-28 (1999)

    • Description
      「研究成果報告書概要(和文)」より
    • Related Report
      2001 Final Research Report Summary
  • [Publications] 大山隆浩, 千木良雅弘, 大村直也, 佐々木和裕, 長岡亨: "不飽和領域での堆積岩の化学的風化作用 泥岩トンネル坑壁の風化速度と微生物の影響"応用地質. 39. 511-523 (1999)

    • Description
      「研究成果報告書概要(和文)」より
    • Related Report
      2001 Final Research Report Summary
  • [Publications] 千木良雅弘: "群発する崩壊 花崗岩と火砕流"近未来社. 200 (2002)

    • Description
      「研究成果報告書概要(和文)」より
    • Related Report
      2001 Final Research Report Summary
  • [Publications] Chigira, M., Nakamoto, M., Nakata, E.: "Weathering mechanisms and their effects on the landsliding of ignimbrite subject to vapor-phase crystallization in the Shirakawa pyroclastic flow, northern Japan"Engineering Geology. (in press).

    • Description
      「研究成果報告書概要(欧文)」より
    • Related Report
      2001 Final Research Report Summary
  • [Publications] Chigira, M.: "Geologic factors contributing to landslide generation in a pyroclastic area : August 1998 Nishigo Village, Japan"Geomorphology. (in press).

    • Description
      「研究成果報告書概要(欧文)」より
    • Related Report
      2001 Final Research Report Summary
  • [Publications] Chigira, M., Inokuchi, T.: "Landslides triggered by August 1998 intense rainfall, northern Japan"Landslide News. (in press).

    • Description
      「研究成果報告書概要(欧文)」より
    • Related Report
      2001 Final Research Report Summary
  • [Publications] Chigira, M.: "Micro-sheeting of granite and its relationship with landsliding specifically after the heavy rainstorm in June 1999, Hiroshima Prefecture, Japan"Engineering Geology. 59. 219-231 (2001)

    • Description
      「研究成果報告書概要(欧文)」より
    • Related Report
      2001 Final Research Report Summary
  • [Publications] Chigira, M. and Oyama, T.: "Mechanism and effect of chemical weathering of soft sendimentary rocks"Engineering Geology. 55. 3-14 (1999)

    • Description
      「研究成果報告書概要(欧文)」より
    • Related Report
      2001 Final Research Report Summary
  • [Publications] Oyama, T. and Chigira, M.: "Weathering rate of mudstone and tuff on old unlined tunnel walls"Engineering Geology. 55. 15-28 (1999)

    • Description
      「研究成果報告書概要(欧文)」より
    • Related Report
      2001 Final Research Report Summary
  • [Publications] Oyama, T., Chigira, M., Omura, N., Sasaki, K., and Nagaoka T.: "Chemial weathering of sedimentary rocks in vadose zone - The weathering rates of mudstone on old unlined tunnel walls and the bacterial effects on it"Jour. Japan Soc. Eng. Geol.. 39, (in Japanese with English abstract). 511-523 (1999)

    • Description
      「研究成果報告書概要(欧文)」より
    • Related Report
      2001 Final Research Report Summary
  • [Publications] Chigira, M., Nakamoto, M., Nakata, E.: "Weathering mechanisms and their effects on the landsliding of ignimbrite subject to vapor-phase crystallization in the Shirakawa pyroclastic flow, northern Japan"Engineering Geology. (In press).

    • Related Report
      2001 Annual Research Report
  • [Publications] Chigira, M.: "Geologic factors contributing to landslide generation in a pyroclastic area : August 1998 Nishigo Village, Japan"Geomorphology. (In press).

    • Related Report
      2001 Annual Research Report
  • [Publications] 千木良雅弘, 中本舞: "気相晶出固化作用を受けた火砕流堆積物の風化と崩壊"日本応用地質学会研究発表会講演論文集. 231-234 (2001)

    • Related Report
      2001 Annual Research Report
  • [Publications] 横山修, 千木良雅弘, 横田修一郎: "シラス風化帯と水文地質学的意義"日本応用地質学会研究発表会講演論文集. 227-230

    • Related Report
      2001 Annual Research Report
  • [Publications] Chigira,M.: "Micro-sheeting of granite and its relationship with landsliding specifically after the heavy rainstorm in June 1999, Hiroshima Prefecture, Japan."Engineering Geology. (In press).

    • Related Report
      2000 Annual Research Report
  • [Publications] Chigira,M.and Inokuchi,T.: "Landslides triggered by August 1998 heavy rainfall, northern Japan."Landslide News. (In press).

    • Related Report
      2000 Annual Research Report
  • [Publications] 諏訪陽子,千木良雅弘: "花崗岩の球状風化について 奈良県柳生花崗岩体を例として"日本応用地質学会平成12年度研究発表会講演論文集. 13-16 (2000)

    • Related Report
      2000 Annual Research Report
  • [Publications] 横山修,千木良雅弘: "南九州に分布するシラスの風化について"日本応用地質学会平成12年度研究発表会講演論文集. 5-8 (2000)

    • Related Report
      2000 Annual Research Report
  • [Publications] 秋山隆弘: "不飽和領域での堆積岩の化学的風化作用-泥岩トンネル坑壁の風化速度と微生物の影響"応用地質. 39. 511-523 (1999)

    • Related Report
      1999 Annual Research Report
  • [Publications] Chigira,M.: "Mechanism and effects of clemical weathering of soft sedimentory rocks"Engireering Geology. 55. 3-14 (1999)

    • Related Report
      1999 Annual Research Report
  • [Publications] Oyama,T.: "Weathering rate of mudstone and teff on old unlined tunnel walls"Engineering Geology. 55. 15-28 (1999)

    • Related Report
      1999 Annual Research Report
  • [Publications] Chigira,M.: "Characteristic weathering profile as basic causes of shallow landslides"Slope Stability Engineering. 2. 1145-1150 (1999)

    • Related Report
      1999 Annual Research Report

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Published: 1999-04-01   Modified: 2016-04-21  

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