We report an experimental study of the surface flow and the creeping flow of glass spheres on a heap. We characterize the dynamics of the flow with particle tracking velocimetry and dynamic light scattering measurements. We observe a creeping flow with a dynamics which slows down exponentially with the depth. The characteristic distance for the decay is one bead diameter. A striking observation is that the exponential decay for the mean velocity holds over more than six orders of magnitude.
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Crassous et al. (2008) studied this question.
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