Characterization of the angle of repose of binary granular materials

Abstract

When a heap or pile of granular material accumulates at the toe of a failed slope, the pile rests at its angle of repose. The gradual build up of a heap of soil in the laboratory simulates the formation of the heap at the toe of a slope. In this study, the angle of repose developed by binary granular mixtures of coarse sand (1.16 mm in average diameter) and fine sand (0.10 mm in average diameter) was measured in the laboratory. The influence on the angle of repose by the roughness of the base on which the mixtures were placed was also investigated. When the mixtures were placed on a rough surface, the heap developed its angle of repose by two different modes of failure. When the mixtures were controlled by the coarse sand fraction, failure took place on a layer located at the free surface of the heap. When the fine sand fraction controlled the composition of the mixture, the heap developed its angle of repose after the material failed by lateral spreading. When the mixture was placed on a smooth surface, the heap developed its angle of repose by a single mode of failure, namely lateral spreading at the interface of the mixture and the smooth base. A theoretical analysis relating the angle of repose, the internal angle friction of the mixtures, and the interface basal friction angle is also presented.Key words: angle of repose, binary granular material, quartz sand, angle of internal friction, interface friction angle, Rankine earth pressure theory.