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Conventional elastoplasticity is based on the idealisation that the interior of the yield surface is a purely elastic domain. This idealisation would not lead to unrealistic prediction of hardening behaviour, but would cause unrealistic prediction of softening behaviour, which is observed typically in overconsolidated soils, whereas metals and normally consolidated soils exhibit hardening behaviour. By contrast, unconventional elastoplasticity that does not use this idealisation makes it possible to describe the plastic deformation due to the change of stress inside the yield surface exhibiting a smooth elastic–plastic transition, and is thus expected to describe softening behaviour more accurately. In this paper the capabilities of conventional and unconventional elastoplasticity for describing softening behaviour are examined, comparing the Drucker–Prager model as the conventional one and the subloading surface model as the unconventional one for predicting the deformation behaviour of overconsolidated soils. It is concluded that unconventional elastoplasticity has to be adopted for predicting softening behaviour.

In this study, a series of incremental loading oedometer tests and microscopic observations is carried out in order to investigate the influence of sand/bentonite fractions on hydraulic conductivity and compressibility. If sand particles do not form a skeletal structure, and each particle is independent in the clay matrix, an additive fraction of sand causes a decrease in the compressibility; however, it does not affect the hydraulic conductivity under the same consolidation pressure. The additive fraction of bentonite contributes to a decrease in the hydraulic conductivity, even for clayey materials. In addition, the relationship between the pore-size parameter, which represents the pore entrance size distribution, and the hydraulic conductivity is discussed using a probabilistic model known as the general capillary model.

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