Focus of this study is on the heterogeneities in laboratory clay samples, which are caused by the presence of completely rough end platens. Non-uniformities in the stress and strain fields of Weald clay samples subjected to drained triaxial and plane strain compressions are assessed by finite element simulations. A three-invariant Cam clay model with volumetric hardening/softening is used to describe the stress-strain behavior of normally consolidated and heavily overconsolidated clay samples. Even though the whole sample nominal stress-strain response is not substantially altered by the friction at the sample-platen interface significant heterogeneities evolve inside the samples. They are caused primarily by non-uniform distributions of the mean effective stress. Local vertical strains at the central portion of the samples greatly exceed 25%, the strain of homogeneously deforming specimens with smooth ends. At the same time the top and bottom outside edges experience small strains and significant stiffening effects due to concentration of the mean effective stress and corresponding decrease in the void ratio. Thus, critical state is reached only at the central part of the samples with the rough ends. In addition, while different types of loading are experienced by different locations inside overconsolidated samples such as a plastic softening, plastic hardening and elastic loading/unloading, in the case of normally consolidated samples all points appear to undergo plastic hardening. The location near the top centerline always experiences some elastic unloading, which is more pronounced in triaxial compression. It is expected that these heterogeneities may play a significant role in initiating the strain localization.
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