Unique determination of cyclic instability state in flow liquefaction of sand

Abstract

Flow liquefaction is a catastrophic failure phenomenon of loose sand when subjected to wave or seismic load, and an instability state can be regarded as the onset of flow liquefaction. Most of the previous studies focused mainly on the static instability state, while the investigations on cyclic instability state (CIS) are very limited and unsystematic. The characteristics of CIS are complex and there is no clear consensus about the determination of CIS. Therefore, this study aims to investigate the characteristics of CIS in flow liquefaction via a series of undrained triaxial tests performed on saturated loose sand. The testing program covers a broad range of initial deviatoric stresses qs , cyclic stress amplitudes qcyc , and relative densities Dr . The test results indicate that CIS will occur at either compressive side or extensive side, depending uniquely on the ratio of qs /qcyc . The slopes of CIS lines increase with an increase in the relative density. Under the same qcyc , the mean effective stress at CIS first decreases and then increases as qs increases. Finally, CIS is predicted by a useful method, which is able to monitor CIS both in situ and in laboratory tests.