Measuring coarse grain deformation by digital image correlation
Résumé
This work presents results from oedometric compression of coarse granular material. Coarse granular media exhibit significant deformations making it complicated to predict the settlement of structures. In this paper, a measurement technique was developed for the analysis of two-dimensional (2D) images of a deforming coarse granular medium to investigate its deformation. This was achieved by realizing grainbased image correlation to measure the grain transformation in gravel with the use of a Digital Image Correlation technique. The 2D displacement fields enable us to explore the behaviour of granular media at different scales: microscopic, mesoscopic, and macroscopic scales. The mesoscopic scale is defined from branches that connect the centres of three neighbouring grains, using a Delaunay triangulation to account for an equivalent continuum media. While the consistency of the macroscopic strain and the average mesoscopic strain is assessed, it is shown that a deviation from the normalized microscopic vertical displacement is an indicator of the heterogeneity of the mesoscopic strain field. The proposed mesoscopic analysis allows us to investigate these heterogeneities. Another important result is that even if the amplitude of the microscopic strain is small (approximately 100 times smaller) compared with the other strain measures, it confirms that the grains are not rigid and that their ultimate strain can be estimated using the proposed approach.
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