[NotiAMCA] postdoc position @ Institut de Physique du Globe de Strasbourg

[Mario Storti]

                        POSTDOCTORAL POSITION
           at Institut de Physique du Globe de Strasbourg,
                   CNRS / Université Louis Pasteur.

Fluidization of saturated granular media : effect of fluid sources and
    seismic waves.
Contact : Renaud Toussaint, CR CNRS, et Jean Schmittbuhl, DR CNRS

Salary : between 2000 and 3000 euros net, according to experience,
     including social security.

Duration: 1 year (starting in 2007 or 2008)

Research project :

Fluidization of water-saturated granular media happens in various
contexts : underwater avalanches, turbidites, landslides after
important rainfall, soil fluidization triggered by seismic
waves. These events are important geophysical alea, with associated
risks causing human and material damage.  During this fluidization,
the pressure rise of the interstitial fluid plays a major
role. Different mechanisms can be activated. Indeed, in a granular
medium, fluids can accumulate over lowly permeable and mechanically
weak barriers, and induce then important deformations by an instable
mobilization of the solid matrix. In the case of a seismic initiation,
the transit of a seismic wave can induce a resonance between the
interstitial fluid flow and the wave propagation, which can fluidize
the material.  We will study this fluidization transitions and
avalanche triggering processes in a laboratory analog model: a
transparent tank mounted on a tilted table. The origin of the
avalanche and fluidization sources considered will be a/ internal
interstitial pressure sources, and b/ seismic wave propagations. The
resulting avalanche nucleation will be imaged using a fast optical
camera (1000 frames/sec), and pressure and flux measuring devices. The
deformation field can be determined using image subtraction techniques
[Lovoll, Toussaint et al 2004, Toussaint, Lovoll et al 2005], and
correlation image velocimetry (CIV) techniques [Chambon, Schmittbuhl
and Corfdir 2003]. The seismic waves will be generated using a 64
channel ultrasonic acoustic station.  This experimental study about
the fluidization transition in a saturated granular medium will be
carried in parallel to a numerical study, based on models of coupled
granular/fluid flows, developed at the host laboratory. These hybrid
discrete granular / continuous fluid models have been recently
developed in the condensed matter physics community [McNamara et al
2000 ] , and have been applied with success to modeling coupled
fluid/granular flows. Notably, they have been applied to situations of
hydrofracturing [Flekkoy et al 2002]. They have also been used with
success to study and reproduce experimental results on the
granular/fluid analog of the Saffman Taylor instability where an
injected fluid displaces the granular medium [Johnsen, Toussaint,
Maloy and Flekkoy 2006], and on the granular Rayleigh Taylor
instability, where an ensemble of dense grains sediment in a lighter
fluid [Vinningland, Johnsen, Flekkoy, Toussaint and Maloy 2006a,2006b
et 2006c].  The research project is then a study of the physical
processes implied in the fluidization of weakly consolidated granular
materials, combining both experimental and numerical approaches.  The
candidate will work on the design and acquisition of experimental
data, and on the implementation of corresponding codes. He can
interact with the experimental geophysics team at IPGS (coming from
rock physics and near surface teams), i.e R. Toussaint,
J. Schmittbuhl, J.P. Malet, A. Remaitre, with other teams of the ANR
project "Triggerland" (LGIT , Grenoble), and with the "Complex" team
of the Department of Physics of the University of Oslo (E.G. Flekkoy,
K.J. Maloy).