Max Wiebicke reçoit le prix de thèse de l’école doctorale IMEP2

The mechanisms that control the macroscopic behaviour of granular soils must be sought at the grain-scale with the interactions of individual particles playing the key-role. To access that scale and describe the fabric of granular assemblies, x-ray micro-computed tomography is used in this thesis for full-field measurements during monotonic and cyclic experiments. As the image analysis techniques used in the past lack a thorough metrological characterisation, it was of crucial importance to study different techniques to determine the fabric and quantify their uncertainties especially considering the inherent limited spatial resolution of tomographies. Artificial as well as high resolution images serve as the basis of a rigorous metrological analysis which showed that the standard approaches for the analysis of contact orientations, implemented in most commercial software, strongly suffer in accuracy and often introduce huge artefacts. Advanced approaches that are shown to produce far less error-prone results are proposed.

Monotonic triaxial compression tests on two different sands are studied regarding the localisation of deformation in terms of the contact fabric. Furthermore, a series of triaxial compression tests with load reversals has been conducted on specimens consisting of sand grains and glass beads. In this case the focus lay on the comparison of the contact fabric response during the load reversals with the evolution of a specific phenomenological state variable, i.e. the inter-granular strain tensor for hypoplasticity.