1986 Fiscal Year Final Research Report Summary
Evaluation of deformation and strength characteristics of sand deposits during earthquakes based on in situ frozen samples
| Project/Area Number |
60460172
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| Research Category |
Grant-in-Aid for General Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Research Field |
Building structures/materials
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| Research Institution | Tokyo Institute of Technology |
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Principal Investigator |
YOSHIMI Yoshiaki Professor, Tokyo Institute of Technology, 工学部, 教授 (90016329)
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| Co-Investigator(Kenkyū-buntansha) |
TOKIMATSU Kohji Associate Professor, Tokyo Institute of Technology, 工学部, 助教授 (50134846)
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| Project Period (FY) |
1985 – 1986
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| Keywords | Sand / Liquafaction / Sampling by in situ freezing / Tube sampling / Shear modulus / N-value / Undrained shear strength / Drained shear strength / Sample disturbance / Deformation characteristics / Dilatancy |
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| Research Abstract |
Laboratoty tests were conducted on samples obtained from sand deposits having different SPT N-values by an in situ freezing method and by an ordinary tube sampling method. Based on the in situ frozen samples, it was observed that (1) the undrained shear strength of saturated sands having the same relative density could vary widely depending on the method and time of deposition of the sand, but (2) a good correlation existed between the undrained shear strength and the SPT N-values corrected for confining stress. The in situ liquefaction resistance of the sands predicted from the laboratoty test results were compatible with the values based on the case histories of liquefaction in the field.
Comparison of the test results of the in situ frozen samples and the tube samples revealed that (1) the static drained strength of the two did not differ much; (2) the undrained shear strengths of the tube samples were considerably lower than those of the in situ frozen samples, the difference being more pronounced as the density increased; and (3) the difference was due to the change in the negative dilatancy characteristics of the sands during sampling.
Additional tests conducted to study the cause of sample disturbance showed that (1) the reduction in the undrained shear strength was mainly caused by shear strain history during sampling, rather than by the release of confining stresses after sampling, (2) the undrained shear strength could markedly be reduced due to shear strain history even when the change in density was negligible, and (3) a good correlation existed between undrained shear strength and shear modulus, suggesting the possibility of evaluating the quality of sand samples on the basis of shear modulus.
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