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Séminaire « Matière molle : organisation et dynamique » de l’INSP

Acoustic probing and triggering of unjamming in dense granular suspensions - Xiaoping Jia - Jeudi 11 mai 2017 à 11 h

INSP - 4 place Jussieu - 75252 PARIS Cedex 05 - Barre 22-32 - 4e étage, salle 407

Xiaoping Jia - Institut Langevin - ESPCI & Université Paris-Est, Marne-la-Vallée


Laboratory studies of granular friction have emerged as a powerful tool for investigating dynamics of seismic faults [1], including dynamics triggering of earthquakes and landslides [2]. However, the physical origin of dynamic wave triggering still remains a challenging issue. Advances in granular mechanics have paved the way for understanding how seismic waves may trigger fault slips. The emerging view is that dynamic perturbation of sheared granular materials causes an elastic softening up to a material failure that could be seen as unjamming transition by the acoustic fluidization [1, 3].

Here I will describe our recent experiments on the unjamming of dense granular suspensions, from a solid-like to a liquid-like state by external vibration. We first investigate the onset of sinking of a steel ball inside a glass bead packing saturated by water under horizontal oscillation (as quicksands). The ball motion being consistent with the frictional rheology is monitored by an ultrasound probing in the opaque suspensions until its arrest, showing that larger is the oscillation amplitude deeper is the sinking depth is [4].

For a better understanding of the vibration-induced fluidization, we then compare this observation with the nonlinear response of a shear wave propagating along the surface of a granular suspension. Two regimes are found when the driving amplitude increases : in the first we observe a significant shear modulus weakening but without visible grain motion, while in the second there is a clear plastic rearrangement of grains accompanied with the modulus decrease up to 85%. We show that these results could be rationalized by a friction model, highlighting the effect of slipping contacts [5].

[1] H.J. Melosh. Nature 379, 601 (1996) ; B. M. Kaproth & C. Marone, J. Geophys. Res. 119, 4821 (2014)

[2] J. Gomberg et al, Nature 411, 462 (2001) ; P. Johnson & X. Jia, Nature 437, 871 (2005)

[3] X. Jia et al, Phys. Rev. E 84, 020301(R) (2011)

[4] S. Wildenberg et al, submitted

[5] J. Brum et al, to be submitted