1. For a general introduction to granular materials, see J. Duran “Poudres et grains” (Eyrolles, Paris 1996).
2. The basic book here is “Physics of blown sand and sand dunes” by E.R. Bagnold (Chapman and Hall, London 1941).
3. H.A. Janssen, Z. Vereins DeutschEng. 39 (35), p. 1045 (1895).
4. Lord Rayleigh, Phil Mag 36, 11, 61, 129, 206 (1906).
5. See for instance “Friction: an introduction”, P. Bowden and D. Tabor (Doubleday, NY 1973).