DIFFUSE VS. LOCALIZED INSTABILITY IN COMPACTING GEOMATERIALS UNDER UNDRAINED CONDITIONS

摘要

The coupling between the pore fluid diffusion and deformation of geomaterials can alter the mechanical response and facilitate or delay material failure. Dilatant or contractive material behavior under conditions of limited drainage and/or of loading rate exceeding the pore fluid diffusion rate causes a reduction or increase in pore pressure, respectively. The latter, via the effective stress principle, results in dilatant strengthening or contractive weakening of frictional materials, namely, an increase or decrease in shear stress that can be sustained by the material from the corresponding value in the underlying drained response. In this work, we use perturbation theory to examine how the contractive weakening affects the stability of undrained deformation and what are the possible instability modes (localized vs. diffuse) on the example of a one-dimensional simple shear of a layer under partially strain-controlled boundary conditions. The effect of material rate-sensitivity on undrained stability is examined.