Extending dilatancy-based constitutive models to hydromechanical response of unsaturated gold mine tailings

ABSTRACT: Hard rock tailings predominantly contain mixtures of low plasticity sand and silt with wide particle size distributions ranging from sub-millimetres to few micrometers. This induces a wide water retention curve spanning over multiple decades of matric suction with potential of significant hydraulic hysteresis during drying and wetting cycles. In some climates and for some deposition schemes, tailings may undergo complex hydro-mechanical stress paths including repeated cycles of drying and wetting. It is now commonly understood that the influence of past desiccation of tailing shear behaviour can be substantive. The partially saturated nature of tailings makes it necessary to adopt proper constitutive models capable of capturing the coupled hydro-mechanical phenomena associated with such regimes. Most commonly used unsaturated constitutive models, such as Barcelona Basic Model and Glasgow Coupled Model (GCM), are developed based on the Cam-Clay theory which is applicable mostly to clayey materials. Hard rock tailings, however, consist of frictional particles whose volumetric response requires a more careful treatment of plastic dilatancy. The current study applies the general framework developed in GCM to a dilatancy-based constitutive model, Norsand, to better capture the behaviour of tailings subjected to desiccation. The model is extended by considering two additional hydraulic yield surfaces and defining appropriate coupling between mechanical and hydraulic processes. The model has been calibrated and used to reproduce triaxial and simple shear tests carried on an unsaturated gold mine tailing. In particular, the accuracy of the model in capturing the main characteristics of the tailings’ shear behaviour is investigated.