X-ray observation of micro-failures in granular piles approaching an avalanche A. Kabla, G. Debrégeas, J.-M. di Meglio and T. J. Senden Europhys. Lett., 71 6 (2005) 932-937 Published online: 10 August 2005 DOI: 10.1209/epl/i2005-10165-4