E3S Web Conf.
Volume 92, 20197th International Symposium on Deformation Characteristics of Geomaterials (IS-Glasgow 2019)
|Number of page(s)||4|
|Section||Laboratory Experimental Techniques: Particle Scale and Fabric|
|Published online||25 June 2019|
Grain kinematics during stress relaxation in sand: not a problem for X-ray imaging
Chalmers University of Technology, Arch. & Civil Eng., SE-41296, Gothenburg, Sweden
2 Univ. Grenoble Alpes, CNRS, Grenoble INP 3SR, F-38000 Grenoble, France
* Corresponding author: firstname.lastname@example.org
X-ray tomography is a very valuable tool for studying the full-field 3D deformation of granular materials. The requirement to stop loading and scan a given state (assumed to be stationary) used in most approaches implies unavoidable stress relaxation during scanning. Since scanning times on laboratory tomographs are normally in the order of 1 hour, the strength of the assumption of a stationary state cannot be tested, which introduces some potential weakness in the interpretation of the rich micro-mechanics observed. This paper presents the kinematics of relaxation of a dry natural sand in a typical oedometric cell used for X-ray scanning, using a synchrotron X-ray source to provide scanning times of around 3 minutes, at two different magnifications. This allows the relaxation of the cell & sand system for the first time to be quantified. Advanced image correlation tools are used to quantify the rearrangements of the soil skeleton during loading and the subsequent relaxation. The results indicate that the magnitude of grain displacements during relaxation, associated to ≈4% reduction in externally measured axial stress under oedometric loading, falls below 0:01D50. It can, therefore, be concluded that the relaxation step required prior to an X-ray scan during an in-situ geomechanical experiment on dry sand does not lead to appreciable uncertainties.
© The Authors, published by EDP Sciences, 2019
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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