The relation between liquefaction resistance and shear wave velocity for new and old deposits

Multiple series of cyclic triaxial tests were performed on undisturbed and reconstituted samples of sandy soils obtained from areas of known liquefaction at the time of the 2011 East Japan Earthquake. In this test scheme, the shear wave velocity was firstly measured and then cyclic loads were applied to determine the cyclic shear strength. The undisturbed samples were classified into two groups, namely, one from old alluvial (Pleistocene) deep deposits and the other from near-surface shallow depths which had apparently been disturbed by the liquefaction in the 2011 event. The data thus obtained were plotted in terms of the cyclic strength versus the shear wave velocity, and two curved lines were drawn through average points in the plot for the two groups of soils, that is, one for the undisturbed soils and the other for the liquefaction-disturbed soils. It was found that for a given cyclic strength, the shear wave velocity does have the propensity to become larger for the undisturbed samples from the old deposits in comparison to the undisturbed samples from the seemingly liquefaction-disturbed samples. Similar sets of laboratory tests were also performed on several sand samples reconstituted to a completely disturbed state. The plots of the test results for these reconstituted samples also showed a tendency in the relation between the cyclic strength and the shear wave velocity which is similar to that for the liquefaction-disturbed samples recovered from the in-situ deposits. In order to understand the outcome of the above observations, the ratio between the cyclic strength and the shear modulus from the shear wave velocity was taken as a parameter to distinguish the two different relations as mentioned above. This ratio, which might be called the “reference strain” of the “yield strain”, is used to provide an interpretation of the difference in correlation between the cyclic strength and the shear wave velocity.