Rotational multiple yield surface framework and the prediction of stress-strain response for saturated and unsaturated soils

Anisotropic soil settlement model known as Rotational Multiple Yield Surface Frame-work characterises soil volume change behaviour from the standpoint of the soil stress-strain relationship. From the stress-strain relationship the soil mobilised shear strength behaviour in saturated and unsaturated conditions is derived in the form of Mohr-Coulomb curved-surface envelope in the space of τ:(σ − u_a ): (u_a − u_w ). Then within this stress space the anisotropic volume change behaviour is characterised from the interaction between the applied stress represented in the form of Mohr circle and soil state of shear strength, τ, in the form of the curved-surface mobilised shear strength envelope. Anisotropic compression is triggered whenever the applied stress state exceeds the strength and the process is stopped when the state of stress equilibrium is reached. This is the condition when Mohr circle just touches the strength surface envelope. The framework utilises the concept of multiple yield surface which is represented by rotation of the mobilised soil shear strength envelope about suction axis towards shear strength envelope at failure as the soil structure is compressed. The rotation of the mobilised shear strength envelope cum the yield surface is to mark the increase in the soil strength which is the direct incorporation of the soil hardening law into the framework. The advantage of this framework is that it directly links the role of shear strength and applied stress in the soil anisotropic volume change response. Consolidated drained triaxial tests have been conducted on saturated and unsaturated specimens of tropical residual soil. The framework prediction of the soil stress-strain response in saturated and unsaturated soil conditions is presented. The close agreement between the experimental and the predicted curves demonstrate the applicability of the framework.