Onset mechanism of granular avalanches in inclining layers using a continuum model

Abstract

• Critical conditions for the onset of macro scale avalanches are presented. • Onset of macro scale avalanches occur in the small area in granular layers. • Stresses and packing fractions reach the maxima at the onset of avalanches. • Both of dilatancy and densification occur at the same time in granular layers. • Aggregates of stick-slip like events are formed in the longitudinal direction. What is the onset mechanism of macro scale avalanches? How do macro scale avalanches happen in the granular layers in an inclining box? The answers to these questions are the main part of our article aims. Using 3-dimensional simulation method we show the stresses, the stress ratios and the packing fractions in the processes where the onset of macro scale avalanches takes place. Based on our results the critical conditions of the onset of avalanches are presented. The onset mechanism of granular avalanches is elucidated. The onset of macro scale avalanches occurs in the small area, about 2% of the whole area, in the inclining granular layers. These are the conditions for the onset of macro scale avalanches that the shear and normal stresses and the packing fraction reach the maximum values at the same inclining angle. Then the stress ratio should be larger than the static frictional coefficient of materials. Aggregates of stick-slip like event are formed in the longitudinal direction. The number of aggregates decreases and the physical quantities in the aggregates rapidly increase with increasing inclining angle in the small area in which the onset of macro scale avalanche occurs.