Rheology of Debris-Ice Avalanches: Insights From the Flow of Bi-Density Mixtures in a Vane Shear Cell

Abstract

Debris-ice avalanches often exhibit higher mobility than debris avalanches, known as hypermobility. Given the increasing destructive power and frequency of such hazards, understanding their rheology could provide insights into their mobility and flow dynamics. Using 3 mm-sized glass and polystyrene beads instead of debris and ice materials, a series of rheological tests was conducted in a vane rheometer at seven different vane speeds on dry specimens with six different polystyrene volumetric contents. The flow dynamics, including the flow curves and the volume change, were evaluated to deduce governing rheological laws. Results reveal that the rheological behavior follows a non-monotonic friction law with a transitional solid-liquid-like behavior and a monotonic dynamic dilatancy law. A density-induced segregation process has been observed, which interplays with rheology. Further analysis of the results demonstrates that, besides the roles of density and the critical state friction parameter, the dynamic dilatancy and segregation process also contribute to enhance the flow mobility of these bi-density mixtures. The proposed rheological laws can be applied to glacier mountain hazard assessment.