| Project/Area Number |
11450179
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| Research Category |
Grant-in-Aid for Scientific Research (B).
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Geotechnical engineering
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| Research Institution | University of Tokyo |
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Principal Investigator |
TOWHATA Ikuo The University of Tokyo, Department of Civil Engineering, Professor, 大学院・工学系研究科, 教授 (20155500)
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| Co-Investigator(Kenkyū-buntansha) |
TATSUOKA Fumio The University of Tokyo, Department of Civil Engineering, Professor, 大学院・工学系研究科, 教授 (70111565)
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| Project Period (FY) |
1999 – 2000
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| Project Status |
Completed (Fiscal Year 2000)
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| Budget Amount *help |
¥13,400,000 (Direct Cost: ¥13,400,000)
Fiscal Year 2000: ¥2,700,000 (Direct Cost: ¥2,700,000)
Fiscal Year 1999: ¥10,700,000 (Direct Cost: ¥10,700,000)
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| Keywords | sand / torsion shear tests / undrained tests / large deformation / viscosity / liquefaction |
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| Research Abstract |
The present study has been attempting to verify that liquefied sand has a rate-dependent nature, as well as directly measuring the viscosity coefficient. This aim has been important because prediction of liquefaction-induced deformation of sandy ground is urgently needed for safety of lifeline facilities as well as river dikes and harbor structures. Model tests have been conducted by many research institutes for this goal and several values of viscosity have been obtained. The shortcoming of this way of study is that model tests cannot directly measure the stress and strain of liquefied sand, and the values of viscosity as back calculated from test results cannot be examined.
With this view point, the present study initiated laboratory shear tests for measuring the viscosity. In the first stage, a hollow cylindrical torsion shear device was employed with little success. The lesson learned from it are ;
- A liquefied specimen forms a water film at its top and consequently torsion shear becomes difficult.
- Moreover, the true state of liquefaction cannot be attained because of dilatancy which under undrained conditions increases the effective stress and makes sand stiff. Accordingly, the second stage of study employed triaxial compression tests in which a possible water film at the specimen ユs top did not affect loading of compressional force. Moreover, it was decided to run tests in a drained manner while controlling artificially the pore pressure high and effective stress low.
The major findings from the study are ;
- The viscosity coefficient of liquefied sand is in the range of 500 to 4000 kPa.
- A dry specimen exhibits a smaller viscosity, suggesting that about 50% of viscosity in a water saturated specimen is generated by pore water ;
probably vortex in pore water among moving sand grains plays an important role.
Alluvial sand with fines has a smaller viscosity than uniformly graded sand.
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