Shear Banding and Crack Propagation in Geomaterials: Clays and Sands

摘要

Under simple and combined stresses clay and sand soils exhibit localization of deformation followed by shear banding. In clays, cracks or fissures and inclusions serve as concentrators when loads are applied to the material. The damage is in the form of one or more shear bands. It is found that for saturated clays the crack helps start shear bands but that it forms and propagates guided by the plasticity of an essentially frictional material. An inclination of 45 - 1/2 phi' with the major principal stress is generally observed. In sands, digital image processing techniques were developed and used to observe the displacements and the development and propagation of the shear bands. Such bands are distributed along the specimens and, upon bifurcation, some coalesce and result in a major band. The inclination of the bands for three sands of different granulometry was found to follow the Arthur-Vardoulakis criterion i.e. 45 + 1/4 (phi' + psi) with major principal stress; phi' and psi being the effective angle of friction and the angle of dilation respectively. Relative density and confining pressures were found to have little or no effects on this inclination. Shear and normal Strain measurements were made within the shear band which was found to change in size with particles moving in and out of it.