Cyclic instability behaviour of sand silt mixture under partial cyclic reversal loading
Flow liquefaction is one of the most catastrophic failure phenomena in geotechnical engineering. It is a form of instability and can be observed during monotonic loading or cyclic loading. It is referred to as static instability/liquefaction for monotonic loading and cyclic instability for cyclic loading. To investigate the link between these behaviours, a number of stress controlled cyclic triaxial tests were carried out on loose sand-silt mixture under cyclic ‘reversal’ and ‘non-reversal’ loading condition. Cyclic reversal loading was partial reversal. Its peak-trough magnitudes were chosen in such a way that cyclic instability was triggered in compression side of the stress space. Thus it gives an opportunity to compare cyclic instability (both for partial ‘reversal’ and ‘non-reversal’) with static instability observed in monotonic loading condition. The test condition covers a range of initial mean effective confining stresses and void ratio. The equivalent granular state parameter was used to synthesize the test results irrespective of fines contents. Test results showed that cyclic instability was governed by the stress ratio at static instability for the same equivalent granular state parameter irrespective of fines contents. Thus, equivalent granular state parameter can be used as a predictor of cyclic instability for cyclic ‘reversal’ and ‘non-reversal’ loading if cyclic instability is triggered in compression side of the stress space.