| Project/Area Number |
63560225
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| Research Category |
Grant-in-Aid for General Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Research Field |
農業土木
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| Research Institution | Gifu University |
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Principal Investigator |
NAKANO Ryoki Gifu Univ., Fac. Agr., Professor, 農学部・生物生産システム学科, 教授 (40135182)
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| Co-Investigator(Kenkyū-buntansha) |
SHIMIZU Hideyoshi Gifu Univ., Fac. Agr., Lecturer, 農学部・生物生産システム学科, 講師 (90144005)
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| Project Period (FY) |
1988 – 1989
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| Project Status |
Completed (Fiscal Year 1989)
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| Budget Amount *help |
¥2,100,000 (Direct Cost: ¥2,100,000)
Fiscal Year 1989: ¥500,000 (Direct Cost: ¥500,000)
Fiscal Year 1988: ¥1,600,000 (Direct Cost: ¥1,600,000)
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| Keywords | Residual strength / Critical state / Fully softened state / Reactivated landslide / Tertiary type landslide / Squeezing tunnel / Clay fraction / Stability analysis / 第三起層地すべり / 完全軟化強度 / 再活動地すべり / 膨張性トンネル / 新第三紀層 / 膨張性土圧 |
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| Research Abstract |
Mechanical properties of tuffaceous mudstones and clays sampled from typical Tertiary type landslides in Niigata Pref. have been investigated mainly from the viewpoint of critical state soil mechanics. Taking advantage of the chance of excavation of Nabetachiyama Tunnel in this landslide zone, severely faulted mudstones have also been sampled and tested. The conclusions are summarized as follows:
1. The water contents of fault clay in the sections suffered from very heavy squeezing pressure of Nabetachiyama Tunnel are in the range of critical or fully softened state corresponding to the effective confining pressure at their depths.
2. The competence factor decreases as the depth of tunnel increases if the mountain to be excavated is severely faulted or folded to critical state. Therefore, the deeper the tunnel formation, the more difficult the tunnel excavation becomes.
3. The natural water content profiles obtained in vertical test pits or by mist borings dug in land-slide zone show high
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values at several depths. Most of these high water contents have also been found to correspond to the water contents at critical state.
4. The residual strength parameters of landslide clay measured by Bromhead type ring shear apparatus purchased with this Grant-in-Aid are always lower than those obtained by reversal direct shear box test carried out with a pendulum type apparatus especially designed for this research. Judging from back analyses of slope stability of reactivated landslide, reversal shear box test gives more reliable residual strength parameters than ring shear test, though an error due to mechanical friction is to be corrected.
5. The angle of friction of landslide clay at residual state and the effective angle of resistance at critical state have a good relationship with CF(Clay Friction) and Ip(Plasticity Index). However, the grain size distribution and Plasticity Index are found to be remarkably affected by pretreatment of the sample. Sonification of the dispersed mud suspension and air drying of the soil sample are recommendable for grain size distribution and plasticity index tests respectively, but sodium hydroxide is not recommendable as a dispersion agent for landslide clay. Less
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