  We study the surface shape of two-dimensional piles using experiments and a
continuum theory for surface flows of granular materials (the BCRE equations).
We first obtain an analytical solution to the BCRE equations with a simple
transformation and show that the surface shapes thereby predicted are in good
agreement with the experimental results. By means of such an analytical
solution, we find that the formation of the curved tails at the bottom of such
piles depends not only on the properties of the granular materials but also on
the drift velocity of the grains within the rolling layer.
