Effects of Non-plastic Fines on Undrained Cyclic Behavior of Loose Sand

Abstract

Currently the occurrence of liquefaction in silty sand (e.g., 1999 Chi-chi Earthquake, repeated liquefaction in Christchurch in 2010 and 2011, and the March 2011 Earthquake in East Japan) has increased the importance of understanding the effect of non-plastic fines on cyclic behavior of sand. The study on their influence has been carried out by several investigators through both field and laboratory tests, obtaining different outcomes that depend on the parameter of comparison. In laboratory testing, void ratio, relative density or sand skeleton void ratio are commonly used for comparing, however, for different fines contents, these values cannot be kept constant at the same time and are no longer representative of particle contact after 30 % of fines. The authors carried out a series of torsion shear tests and a comprehensive review of previous studies and their results is presented and explained in this work, considering a micromechanical interpretation to omit the use of void ratio and relative density. In this regard, a different approach was used by comparing compaction energy during sample preparation which intends to simulate natural conditions. Sand retrieved from Tokyo Bay area after the liquefaction events of March 2011, was used to conduct monotonic and cyclic tests in a hollow shear torsional apparatus with fines varying from 0 to 80 %. Differences observed in stress–strain curves, effective stress paths and excess pore pressure distribution, are shown. Moreover, liquefaction curves and relevant conclusions regarding the effect of fines content are provided. It was found that the liquefaction resistance and other mechanical properties are basically deteriorated by adding more non-plastic fines, although a certain fluctuation occurs. Finally, these results are used to conciliate different conclusions presented in past literatures.