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Explanation of Seepage Failure Mechanism at Steep Slope of Shirasu Soil

Research Project

Project/Area Number 11460114
Research Category

Grant-in-Aid for Scientific Research (B).

Allocation TypeSingle-year Grants
Section一般
Research Field Irrigation, drainage and rural engineering/Rural planning
Research InstitutionKagoshima University

Principal Investigator

MIWA Koichi  Kagoshima Univ., Fac.Agriculture, Professor, 農学部, 教授 (40032099)

Co-Investigator(Kenkyū-buntansha) WAKAMATSU Chiaki  Kagoshima Univ., Fac.Agriculture, Assistant Professor, 農学部, 講師 (70041647)
MOMII Kazuro  Kagoshima Univ., Fac.Agriculture, Assoc.Professor, 農学部, 助教授 (40136536)
CHO Katsushi  Kagoshima Univ., Fac.Agriculture, Professor, 農学部, 教授 (20038235)
HIRA Mizuki  Kagoshima Univ., Fac.Agriculture, Research Associate, 農学部, 助手 (40284913)
Project Period (FY) 1999 – 2000
Project Status Completed (Fiscal Year 2000)
Budget Amount *help
¥7,200,000 (Direct Cost: ¥7,200,000)
Fiscal Year 2000: ¥1,400,000 (Direct Cost: ¥1,400,000)
Fiscal Year 1999: ¥5,800,000 (Direct Cost: ¥5,800,000)
KeywordsShirasu slope / Seepage failure / Internal stability / Fractal dimension / Piping / Critical gradient / 伸張特性 / 浸透経路 / 噴気孔跡 / 限界動水勾配
Research Abstract

To clarily the mechanism of seepage failure at the steep slope of Shrasu (pyroclastic flow deposit), further works are required to study on undisturbed samples. However, the following conclusion can be drawn from piping tests of disturbed samples.
Soil particles can migrate within the interstics of a skelton structure, and can be washed out from the surface of slope if subjected to a sufficient hydraulic gradient. This is the first stage of seepage failure. A soil will be described as having stable gradation if it does not lose the particles, whereas it has an unstable gradation if particles can casily be lost.
To determine whether Shirasu soil was on internal stability or not, the useful limit was proposed in this research that Shirasu soil having a fractal dimension D≦2.4 was a stable state coresponding to unifomity coefficient Uc≧20 and stability index H/F≦1.3 and these having D≧2.4 was liable to be unstable, where D was derived from the shape of the grain-size distribution curve. According to this new limit, third fifth of Shirasu were unstable states. In this condition, the strong piping of fines took place at gradients of almost one half to two third of the critical gradient given by the clasical piping theory.
Therefore the process of failure at the cliff can be smmurized as follows ; the fines are washed out and the small seepage hole is formed by piping. After that, the hole is enlarged with the erosion at the bottom of the holes as coming off in thin section like mica around the hole. And then the part above it slides suddenly down by its own weight.

Report

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

    (11 results)

All Other

All Publications (11 results)

  • [Publications] 三輪晃一: "シラス急斜面に発生する浸透破壊"自然災害科学研究西部地区部会報 研究論文集. 25. 179-182 (2001)

    • Description
      「研究成果報告書概要(和文)」より
    • Related Report
      2000 Final Research Report Summary
  • [Publications] 三輪晃一: "災害復旧された擁壁に作用する主働土圧について"鹿児島大学農学部学術報告. 51. 37-41 (2001)

    • Description
      「研究成果報告書概要(和文)」より
    • Related Report
      2000 Final Research Report Summary
  • [Publications] Koichi Miwa: "Seepage Failure Occurred in Steep Slope of Shirasu"Western Regional Division Report of Japan Group for Study of Natural Disaster. No.25. 179-182 (2001)

    • Description
      「研究成果報告書概要(欧文)」より
    • Related Report
      2000 Final Research Report Summary
  • [Publications] Koichi Miwa: "Active-earth Pressure on Reconstructed Retaining Wall"Bulletin of Faculty of Agriculture Kagoshima University. No.51. 37-41 (2001)

    • Description
      「研究成果報告書概要(欧文)」より
    • Related Report
      2000 Final Research Report Summary
  • [Publications] 三輪晃一: "シラス急斜面に発生する浸透破壊"自然災害科学研究西部地区部会報 研究論文集. 25. 179-182 (2001)

    • Related Report
      2000 Annual Research Report
  • [Publications] 三輪晃一: "災害復旧された擁壁に作用する主働土圧について"鹿児島大学農学部学術報告. 51. 37-41 (2001)

    • Related Report
      2000 Annual Research Report
  • [Publications] 平 瑞樹、三輪晃一他3名: "斜面に垂直な浸透力によるシラス崖錐堆積物の破壊条件"農業土木学会論文集. 190. 21-26 (1997)

    • Related Report
      1999 Annual Research Report
  • [Publications] Miwa Koichi他2名: "Stability of Shirasu Talus Deposit Due to Inflow and Outflow Normal to Slope."Soils and Foundations. 37・4. 127-131 (1997)

    • Related Report
      1999 Annual Research Report
  • [Publications] 平 瑞樹、三輪晃一他2名: "鹿児島県北西部地震による農地・農業用施設の被害"自然災害西部地区部会報・論文集. 22. 39-44 (1998)

    • Related Report
      1999 Annual Research Report
  • [Publications] 平 瑞樹、三輪晃一他1名: "出水市針原川土石流による農地被害"自然災害西部地区部会報・論文集. 22. 239-243 (1998)

    • Related Report
      1999 Annual Research Report
  • [Publications] Mizuki Hira他2名: "Elasto-Plastic Deformation of Compacted Shirasu"Mem.Fac.Agr.Kagoshima Univ.. 34. 135-142 (1998)

    • Related Report
      1999 Annual Research Report

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

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