Large strains in cemented granular aggregates: Elastic-plastic cement

Abstract

Abstract We describe large-strain behavior of cemented geomaterials by modeling the deformation of a random pack of identical cemented spheres. In this model we assume that the grains are elastic but that the intergranular cement becomes partly plastic as local stresses meet a plasticity condition. This plasticity condition for a thin elastic-plastic cement layer is derived based on the von Mises criterion. Next we solve the problems of large-strain deformation of two cemented spheres in compression and in shear. This solution allows for calculation of the normal and shear strain-dependent stiffnesses of two cemented grains. Finally, we derive effective stress-strain laws for an aggregate of cemented spheres where grain-to-grain contact stiffnesses are strain-dependent. These theoretical stress-strain laws are close to the relations typically observed in clay-cemented sands. An important result is that an initially isotropic aggregate may become anisotropic if the stress field is non-hydrostatic. This stress-induced anisotropy may lead to an up to 10% error in estimating, for example, an apparent isotropic bulk modulus from a uniaxial-strain experiment.