Study on factors affecting Iiquefaction properties of natural sandy soils containing fines and their evaluation procedures

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Liquefaction properties of sandy ground under its natural state are not well understood. For example, the relationship between the SPT N-value and the liquefaction resistance of sands containing fines has been derived from a limited number of data, and thus its applicability is not yet fully verified. The in-situ freezing sampling method, which is believed to be the most reliable technique, is not the exception, since the retrieved sample may be disturbed to certain extents due to the possible volume expansion of pore water during the freezing process, in particular with sands containing larger amount of fines The details of the time effect that may cause changes in the soil particle structures are not known either. In view of the above, in the present study, experimental investigations are conducted on three kinds of in-situ frozen samples and their reconstituted specimens, focusing on their different degrees of time effects and possible link between the liquefaction properties and the small strain properties. As a result, the small strain stiffness and the liquefaction resistance of the in-situ frozen sample were larger than those of the corresponding reconstituted specimen. The difference was larger with Pleistocene samples than with Holocene sample, reflecting the time effects. By applying a large number of cyclic loading history on reconstituted specimens in advance under drained condition, these properties could be improved, while they could not be restored to the levels of the in-situ frozen samples in case of the Pleistocene ones. In addition, large strain properties of these samples after liquefaction on the order of several tens of percent could be evaluated by using a modified version of hollow cylindrical torsional shear apparatus. Effects of the level of confining pressure that is applied to in-situ frozen samples during their thawing process on the liquefaction properties could be also revealed.