Measuring rockfill deformation by digital image correlation
Mesure de la déformation des enrochements par corrélation d'images numériques
Résumé
In this paper, we present the results of an experimental study based on the development on a Digital Image Correlation (DIC) tool to analyse strain of a rockfill media under oedometric compression. The study of granular materials containing large particles such as rockfill requires suitable laboratory facilities whose dimension must be in proportion to the maximum size of the grains. The oedometric cell used here has been developed by IRSTEA laboratory in Aix-en-Provence (France) and has a square surface of 30cmx30cm and is 40cm high, whereas the grains have a maximum size of 4cm. Some of the cell walls are in Plexiglas, to guarantee the optic accessibility of surfaces. DIC techniques are then used to measure the grains displacements field in 2D and in 3D using 2 cameras. To compute strain, the assembly is replaced by a continuous domain, and displacement of the characteristics points of the equivalent continuum media is equal to the displacement of the particles centres. To define local strain, a meso-scale is defined, whose branches connect the centres of three particles in contact, using Delaunay triangulation. The rotation of each grains is also up-scaled for higher order continuum model evaluation. The gradient of the displacement field of each triangle is then determined on the basis of particle displacements and microlevel geometrical characteristics
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