Void ratio evolution inside shear bands in triaxial sand specimens studied by computed tomography

A study of strain localization in triaxial tests on sand, using computed tomography is reported, The inception and the development of the localization are detected and described, both qualitatively and quantitatively, The complex geometrical structures involved in the localization patterns are described and the local void ratio evolution in the localization zone(s) is determined, Dense and loose Hostun RF sand specimens were tested under a confining pressure of 60 kPa, It is shown that strain localization can occur in different localization patterns depending on test conditions; a mechanism involving, simultaneously, a central cone and a set of planes in pairs was found for many of the specimens tested, The comparison of the local void ratio evolution in the shear zones with the global void ratio measurement supports the important conclusion that a limit void ratio is reached in the shear zones, This ratio is significantly different from the final void ratio defined from the global measurements; the lack of physical relevance of the latter is established.