A liquefaction criterion for fine-grained sand constituting Nam O formation subjected to uni-directional and multi-directional cyclic shear

Abstract

In this paper, fine-grained samples at nominally 50% relative density of Nam O sand were tested using several series of uni-directional and multi-directional cyclic shears. The changes of cyclic shear-induced effective stress reduction were observed for a wide range of shear strain amplitudes and various cyclic shear directions and number of cycles. The effects of such cyclic shearing conditions on the liquefaction resistance of the soil were then clarified. It is indicated from experimental results that the effective stress in Nam O sand reduces quickly by the application of the cyclic shear and that the soil is liquefied even when the cyclic shear strain is at small amplitude (y = 0.1%). The effects of cyclic shear direction on the effective stress reduction and also on the liquefaction resistance of the soil are evident at small shear strain amplitude; these effects, however, decrease with y and become negligible when y >= 1.0%, at which the soil is liquefied after a very few numbers of cycles. The occurrence of liquefaction in Nam O sand can be observed precisely for various cyclic shear directions by using relations between the shear strain amplitude and the number of cycles. The liquefaction criterion of Nam O sand was finally obtained and discussed for both cases of uni-directional and multi-directional cyclic shears.