An elasto-plastic modeling for structured and overconsolidated soils

The original Cam-clay model was newly placed not on the classical but on the "unconventional plasticity" theory by introducing super and subloading yield surfaces. The former yield surface lies outside the Roscoe Surface and describes the structured state, while the latter exists inside the superloading yield surface and describes overconsolidated state. This extension of the original Cam-clay model was made in order to describe mechanical behavior of naturally deposited soils. Both the loss of structure and the decay of overconsolidation proceed with ongoing plastic shear deformation, but the former proceeds at a much slower phase than the latter in natural clay, which could triggers off delayed compression/consolidation. The decay of overconsolidation in sand proceeds more slowly than the loss of structure, which causes hardening with plastic volume expansion above the classical critical state line.