Solving boundary value problems requires implementation of sufficiently robust constitutive models. Most models try to incorporate a great deal of phenomenological ingredients, but this refining often leads to overcomplicated formulations, requiring a large number of parameters to be identified. On the other hand, geomaterials are known to have an internal microstructure, made up of an assembly of interacting particles. Most of the macroscopic properties, observed on a specimen scale or even on larger scales, mainly result from the microstructural arrangement of grains. Thus, a powerful alternative can be found with micromechanical models, where the medium is described as a distribution of elementary sets of grains. The emergent complexity is not related to the constitutive description, but to the basic topological properties taking place on the microscopic scale. This presentation discusses this issue, showcasing very recent results obtained from discrete element simulations. Then, an advanced micromechanical model (3D-H model) is presented. It introduces an intermediate scale (mesoscopic scale) made up of a set of adjoining particles. This new approach makes it possible to recover many constitutive properties observed on the macroscopic scale in a very natural way, such as the occurrence of diffuse versus localized failure modes. Some recent numerical results obtained from FEM computations are presented in order to give clear insights into the capability of such multiscale approaches to deal with engineering scales in the future. In particular, failure occurrence within soil masses or geo-structures is thoroughly discussed.
Dr. F. Nicot received his Engineer and PhD degrees in civil engineering in 1995 and 1999, respectively, at Centrale School of Lyon (France). As a world-renowned researcher in soil mechanics, his activities deal with geomechanics, with a special focus on micromechanics of granular materials and multiscale failure modeling. Application fields span from constitutive modeling of geomaterials to gravity-driven natural hazards analysis, including slope engineering issues. He has published more than 200 articles, including 125 papers in international journals together with more than 20 collective books.
He is co-director of the International Research Network GeoMech (Multi-Physics and Multi-scale Couplings in Geo-environmental Mechanics), gathering more than 25 academic institutions over the world. He is currently Editor-in-Chief of the European Journal of Environmental and Civil Engineering (T&F Publ.), and he is Associate Editor of Granular Matter (Springer Publ.)