X-ray microtomography characterisation of the changes in statistical homogeneity of an unsaturated sand during imbibition

Abstract

International audienceThis paper deals with determination of the size of the representative volume element (RVE) of an unsaturated sand specimen and its evolution during wetting. An imbibition test was conducted in an oedometer cell while stepwise reducing the capillary pressure by using the negative water column technique. X-ray tomography scans were acquired at each equilibrium state and three-dimensional images of a partial volume of the specimen were processed. Characterisation of the sample's homogeneity was based on the asymptotic behaviour method for three quantities of interest: the air fraction and the median diameters of both the air and the water-grain phases obtained from Matheron's granulometry. It is shown that the RVE size depends on the choice of the quantity of interest and evolves with the saturation state

Basic Mechanical Properties of Wet Granular Materials: A DEM Study

“…The present paper states some essential results obtained by DEM simulations, for both isotropically compressed static assemblies, and I-dependent steady uniform shear flows, with special emphasis on the critical state in the limit of I → 0, in the case of a model of wet spherical grains. Compared to similar numerical studies in the literature (Richefeu et al 2006;Scholtès et al 2009b) the ones presented here investigate looser structures, which could not be observed with dry grains -as evidenced in experiments with sands (Bruchon et al 2013a;Bruchon et al 2013b). While both situations should be more extensively studied, in more detailed publications (Khamseh et al 2015;Than et al 2015), in which thorougher investigations of microscopic aspects will be presented, some salient features of isotropic compression and steady shear flows are described, stressing the differences with dry, cohesionless materials.…”

A micromechanicalμUNSAT effective stress expression for stress-strain behaviour of wet granular materials

“…3. Imaging techniques such as computed tomography indeed are very promising in allowing precise measurements of the fluid phase microstructures [17,18]. Then, one would be able to compute the microstructure tensors µ X in Eq.…”

“…To address this shortcoming, the present paper first recalls in Section 2 the µUNSAT expressions that enable one to indirectly access the contact stress through capillary stresses and the fluid phase microstuctures, whose measurements appear to be more feasible thanks to e.g. computed tomography [17,18]. For the purpose of the paper, the choice is actually made to con-sider a Discrete Element Method (DEM) model for wet granular materials [19], presented in Section 3, which allows both direct and indirect measurements of the contact stress from a comprehensive description of the microstructure of all solid and fluid phases, including interfaces.…”

Mesostructure Evolution of Gravelly Soil under the Triaxial Compressive Condition by Computerized Tomography

“…In addition, the technique of X-ray computerized tomography (CT) imaging has been well developed, which has been used to visualize and quantify the soil structure at different scales based on its reliable and nondestructive evaluation of images at a high resolution [5,6]. With the help of CT technology, some investigations were conducted to perform the material microstructure analysis [7][8][9][10], including physical density and void ratio measurement [11][12][13][14][15], determining the aggregate size distribution of soil [16], and the numerical model establishment of geotechnical materials [17]. Meanwhile, some research achievements on the mesodeformation mechanism of granular materials have been performed by using CT technology.…”