We describe large-strain behavior of cemented geomaterials by modeling
the deformation of a random pack of identical cemented spheres. In th
is model we assume that the grains are elastic but that the intergranu
lar 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 compre
ssion and in shear. This solution allows for calculation of the normal
and shear strain-dependent stiffnesses of two cemented grains. Finall
y, 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 typi
cally observed in clay-cemented sands. An important result is that an
initially isotropic aggregate may become anisotropic if the stress fie
ld is non-hydrostatic. This stress-induced anisotropy may lead to an u
p to 10% error in estimating, for example, an apparent isotropic bulk
modulus from a uniaxial-strain experiment.