Equivalent granular state parameter and undrained behaviour of sand-fines mixtures

State parameter defined using void ratio, e, and the steady-state line has been shown to be effective in predicting the undrained behaviour of sand. However, steady-state line for sand with fines is dependent on fines content. To overcome this problem, the concept of equivalent granular void ratio, e*, has been well investigated. However, the conversion from e to e* has been essentially a back-analysis process. A methodology for converting e to e* without the need of a back-analysis process was first presented. The concept of equivalent granular state parameter, psi*, defined in terms of e*, and equivalent granular steady-state line was then developed. An extensive experimental study was conducted to investigate whether psi* can capture the effects of fines content, and thus can be used to correlate undrained behaviour of sand-fines mixtures without the need of separately considering the effects of fines content. This study suggested that the effective stress path and deviatoric stress-strain responses in undrained shearing can be correlated with the psi* value at the start of undrained shearing irrespective of fines content.