When dealing with unsaturated wet granular materials, a fundamental question is: What is the effect of capillary cohesion on the bulk flow and yield behavior? We investigate the dense-flow rheology of unsaturated granular materials through experiments and discrete element simulations of homogeneous, simple annular shear flows of frictional, cohesive, spherical particles. Dense shear flows of dry, cohesionless granular materials exhibit three regimes: Quasistatic, inertial, and intermediate [B. Andreotti et al., Contemp. Phys. 55, 151–152 (2013)]. Herewith, we show that the quasistatic and the intermediate regimes persist for unsaturated materials and that the rheology is essentially described by two dimensionless numbers: The reduced pressure P* comparing the cohesive to confining forces and the inertial number I, for a wide range of liquid content. This is consistent with recent numerical simulations [S. Khamseh et al., Phys. Rev. E 92, 022201 (2015)]. Finally, we measure the effective friction coefficient and the solid fraction variation throughout the wet bed. From this, we show that, in the quasistatic regime, the Mohr–Coulomb yield criterion is a good approximation for large enough P*. The experimental results agree quantitatively with the numerical simulation ones, provided the intergranular friction coefficient μ is set to its physical value identified from dry material rheology [M. Badetti et al., Eur. Phys. J. E 41, 68 (2018)]. To directly and quantitatively determine what happens inside the sheared granular bed, x-ray tomography measurements are carried out in a custom-made setup that enables imaging of a wet granular material after different shear histories. For the explored range of liquid content, samples remain homogeneous but exhibit some complex microscopic morphologies far from simple capillary bridges. From the x-ray microtomographic images, we can clearly distinguish liquid capillary bridges and liquid clusters by their morphologies. We see that the total number of capillary bridges decreases when one increases the liquid content and interestingly increases, at the expense of other morphologies, when we increase the shear strain. This explains the concordance between the experimental and numerical measurements since the numerical model is restricted to the pendular state, for which the liquid phase is completely discontinuous and no coalescence occurs between liquid bridges.
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September 2018
Research Article|
September 01 2018
Rheology and microstructure of unsaturated wet granular materials: Experiments and simulations
M. Badetti;
M. Badetti
Laboratoire Navier (UMR 8205, CNRS, IFSTTAR, Ecole des Ponts ParisTech), Université Paris Est
, 2 Allée Kepler, Cité Descartes, F-77420 Champs-sur-Marne, France
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A. Fall;
A. Fall
a)
Laboratoire Navier (UMR 8205, CNRS, IFSTTAR, Ecole des Ponts ParisTech), Université Paris Est
, 2 Allée Kepler, Cité Descartes, F-77420 Champs-sur-Marne, France
a)Author to whom correspondence should be addressed; electronic mail: abdoulaye.fall@ifsttar.fr
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D. Hautemayou;
D. Hautemayou
Laboratoire Navier (UMR 8205, CNRS, IFSTTAR, Ecole des Ponts ParisTech), Université Paris Est
, 2 Allée Kepler, Cité Descartes, F-77420 Champs-sur-Marne, France
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F. Chevoir;
F. Chevoir
Laboratoire Navier (UMR 8205, CNRS, IFSTTAR, Ecole des Ponts ParisTech), Université Paris Est
, 2 Allée Kepler, Cité Descartes, F-77420 Champs-sur-Marne, France
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P. Aimedieu;
P. Aimedieu
Laboratoire Navier (UMR 8205, CNRS, IFSTTAR, Ecole des Ponts ParisTech), Université Paris Est
, 2 Allée Kepler, Cité Descartes, F-77420 Champs-sur-Marne, France
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S. Rodts;
S. Rodts
Laboratoire Navier (UMR 8205, CNRS, IFSTTAR, Ecole des Ponts ParisTech), Université Paris Est
, 2 Allée Kepler, Cité Descartes, F-77420 Champs-sur-Marne, France
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J.-N. Roux
J.-N. Roux
Laboratoire Navier (UMR 8205, CNRS, IFSTTAR, Ecole des Ponts ParisTech), Université Paris Est
, 2 Allée Kepler, Cité Descartes, F-77420 Champs-sur-Marne, France
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a)Author to whom correspondence should be addressed; electronic mail: abdoulaye.fall@ifsttar.fr
J. Rheol. 62, 1175–1186 (2018)
Article history
Received:
February 26 2018
Accepted:
July 11 2018
Citation
M. Badetti, A. Fall, D. Hautemayou, F. Chevoir, P. Aimedieu, S. Rodts, J.-N. Roux; Rheology and microstructure of unsaturated wet granular materials: Experiments and simulations. J. Rheol. 1 September 2018; 62 (5): 1175–1186. https://doi.org/10.1122/1.5026979
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