Stress, voidage and velocity coupling in an avalanching granular heap

Abstract Slowly poured granular heaps evolve by a process of discrete avalanching. We separately investigate stress and voidage evolution in the dynamic boundary layer in which avalanching is initiated and takes place and patterns of stress distribution in the static regions of the heap which are not involved in avalanche activity. The defining events in the evolution of the heap are limited in number and localised in time and space. We investigate stress, voidage and avalanche velocity coupling, particularly in terms of these localised defining events. We analyse the time series that result from periodic sampling of a granular dynamics simulation and demonstrate the potential of the discrete wavelet transform that has been added to our simulation post-processing toolset as an aid to coupling of time series variables in the context of localised defining events. In particular, we show that correlation between time-lagged wavelet transform coefficients can be much more revealing than correlation functions derived from the original time series themselves and has the potential to identify time constants in the absence of clearly defined periodicity.