Study on effects of aging and fine contents on liquefaction characteristics of sands

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A new triaxial testing apparatus wich can change the axial strain continuously about three orders of magnirude was developed, and a series of cyclic triaxial tests was performed on several sands prepared at different conditions.Based on results of drained cyclic triaxial tests, on Toyoura sand, it was reconfirmed that the drained vertical Young's modulus is basically a function of the effective vertical stress. By assuming such stress-induced anisotropy in modeling of elastic deformation charcteristics for sands and correcting for the effects of initial anisotropy and membrane penetration, it was demonstrated that change of elastic behavior during liquefaction process which was measured by undrained cyclic triaxial tests can qualitatively be explained. On the other hand, it was also shown that some quantitative discrepancies exist, especially at triaxial extension condition, between the measured and predicted elastic behaviors during liquefaction process.Based on test results on artificial samples, prepared by mixing Toyoura sand and bentonite at a ratio of 95% and 5% in dry weight, it was shown that longer consolidation time or higher temperature during consolidation results in increase in its liquefaction resistance. Based on tests results on undisturbed samples with a fines content of 6%, retrieved by in-situ freezing sampling from a Holocene sandy soil layr with a SPT-N value of 33 located at a depth of 11.5m, it was shown that the relationship between its liquefaction resistance and the SPT-N value, corrected for the effect of overburden pressure, is consistent with those obtained by previous studies, while the measured value of vertical Young's modulus is smaller than that evaluated from the results of in-situ elastic wave velocity surveys. It was also shown that, for these two samples, the change of elastic behavior during liquefaction process is qualitatively similar to that aforementioned for Toyoura sand.