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We have all experienced jamming. Salt grains flowing though the holes of the salt cellar jam often. Similar phenomena occur in the traffic, in stampedes, and in many industrial processes. From a practical point of view, it is known that if spherical grains are discharged though an aperture at the bottom of a silo, jamming does not occur if the hole is larger than 5 times the size of the grains (assuming humidity is rather low). In cooperation with the granular research group of the University of Navarra, we have developed experiments to study this process in 3D and 2D silos. We have found that the distribution of avalanche sizes (amount of material flown between two consecutive jams) is exponential in all cases. However, 3D and 2D silos behave differently. In 3D silos, we can define a critical aperture size beyond which jamming does not happen, whereas 2D silos seem to eventually jam for any size of the orifice.


  1. Journal of Statistical Mechanics: Theory and Experiment P04008 (2012): R. O. Uñac, A. M. Vidales, L. A. Pugnaloni, The effect of the packing fraction on the jamming of granular flow through small apertures
  2. Physical Review E 80, 011309_1-011309_7 (2009): C. Mankoc, A. Garcimartín, I. Zuriguel, D. Maza, L.A. Pugnaloni, Role of vibrations in the jamming and unjamming of grains discharging from a silo
  3. Europhysics Letters 84, 44002_1-44002_6 (2008): A. Janda, I. Zuriguel, A. Garcimartín, L.A. Pugnaloni, D. Maza, Jamming and critical outlet size in the discharge of a two-dimensional silo
  4. Physical Review E 71, 051303_1-051303_9 (2005): I. Zuriguel, A. Garcimartín, L.A. Pugnaloni, J.M. Pastor, D. Maza, Jamming during the discharge of granular matter from a silo
  5. Physical Review E (Rapid Communications) 68, 030301-030304 (2003): I. Zuriguel, L.A. Pugnaloni, A. Garcimartín. D. Maza, Jamming during the discharge of grains from a silo described as a percolating transition