Soil model to study PVD on soft clay

Question

Which of the following will be the best-suited soil model to study the shear strength gain from the ground improvement by prefabricated vertical drains? Can anyone compare the Modified Cam Clay (MCC) model and Soft Soil Model to find the better one for this case?

Faseel Khan · Answer

If proper initial stress conditions are established then the Modified Cam Clay (MCC) model would give more or less similar results as the Soft Soil (SS) model. As far as the use of MCC model is concerned, the MCC model may allow for unrealistically large ratios of shear stress over mean stress when the stress state is above the critical state line. Furthermore, these models predict a softening behavior for the state of stress on the dry side of the yield surface. Without special considerations, the softening behavior leads to mesh dependency of a finite element analysis. The use of this model in simulations of practical applications including general boundary value problems is not recommended. In the SS model, the volumetric mechanism that captures the compressibility and volumetric hardening (densification) of the material is simulated by an elliptical cap that is very similar to the MCC model. Since soft soils do not show a significant dilation while shearing, the dilation angle for this mechanism in the SS model is usually set to zero. Therefore the better choice here would be the SS model.