Predicting undrained static response of sand with non-plastic fines in terms of equivalent granular state parameter

The influence of non-plastic fines on undrained monotonic behaviour of sand was investigated over a wide range of fines content (FC = 0-40%), global void ratio and initial mean effective stress (p0 ' = 100 kPa to 500 kPa), by performing triaxial compression tests with isotropic and anisotropic consolidation. For the sand-silt mixtures, steady-state line in the e - log(p ') space was found to be dependent on fines content with the existence of a limiting fines content, which defines the transition from a "fines in sand" to a "sand in fines" soil fabric. It is demonstrated that by means of the concept of equivalent granular void ratio, e*, all steady-state/critical state data points can be well described by a unique relationship in the e* - log(p ') space called the equivalent steady-state line (EG-SSL), regardless of fines content. The equivalent granular state parameter (psi*), defined in terms of e*, and the EG-SSL can be effectively adopted for predicting the undrained monotonic behaviour of sand-silt mixtures and the onset of static instability, irrespective of fines content and initial state of the sand-silt mixtures.