Advanced hydro-mechanical coupling for unified constitutive modelling of unsaturated soils

A new unified constitutive hydro-mechanical model named ACMEG-s is formulated to improve modelling of unsaturated soils in free or constrained conditions. Indeed, due to particular mechanical and hydraulic boundary conditions, some natural and engineered fine grained soils are highly constrained. When submitted to in-situ wetting-drying cycles, such soils are prone either to collapsing or to generating swelling pressures. The proposed unified framework provides a direct explanation for complex confined behaviour of unsaturated soils. A sophisticated saturated model based on two coupled plastic mechanisms has been extended to deal with partially saturated states. The adopted stress framework includes a Bishop-type effective stress for the mechanical part and the matric suction for the hydraulic part. Some simplifications brought by the socalled generalised effective stress representation versus conventional net stress and suction representation are overviewed and related to the definition of the ‘Loading Collapse’ yield curve. Other implications of the unique mechanical stress associated with suction couplings are shown to be essential in prediction. The most pioneering results from the model validation by integration via a custom numerical tool are exposed. The combination of the advanced yet simple stress framework and the adapted yield locus is used for the prediction of oedometric and constant volume tests, leading to a straightforward interpretation of swelling pressure tests.