Observation of strain localization by digital image correlation to study the influence of particle size distribution

Strain localization is a pervasive phenomenon observed in many materials and characterized by a loss of homogeneity of the field of deformation. In the particular case of geomaterials, this feature often occurs in the form of shear bands observed on outcrops or accompanying the failure of cavities, landslides or fault zones. The characterization of the size of the zone where most of the deformation concentrates is therefore a key parameter to the design of geostructures and the understanding of many natural hazards. It influences also the strength weakening of the material and many multi-physical processes as it affects the temperature increase or the pore pressure evolution. In this study, we focus on the characterization of the influence of the microstructure size on the shear band thickness. Triaxial experiments have been conducted on a silicate sand presenting different particle size distributions: graded and uniform. The shear band thickness evolution is estimated by Digital Image Correlation (DIC) using cameras placed around the triaxial cell. From the field of deformation, a gaussian distribution has enabled to fit the data satisfactorily. The width of the shear band exhibits a rapid decrease until reaching a residual value depending only on the mean grain size.