New insight into the unified hydro-mechanical constitutive modeling of unsaturated soils

Besides the so-called conventional features of behaviour of unsaturated soils, in-situ analyses evidence complex constraining and confining conditions for media submitted to wetting drying cycles. In an effort to simulate the hydro-mechanical coupling effects raised by these particular mechanical conditions, an advanced constitutive model is formulated on the basis of a unified stress framework. The model formulation derives directly from the understanding of mechanisms of behaviour of partially saturated material submitted to alternative combinations of mechanical and hydraulic loading in laboratory. The adopted stress framework is a Bishop-type effective stress for the mechanical part and the matric suction for the hydraulic part. Simplifications brought by the effective stress representation versus conventional net stress and suction representation are exposed and related to the definition and multiple use of the ‘loading collapse’ curve. The most pioneering results from the model validation by integration via a custom numerical tool are exposed, with a particular attention paid to back prediction of oedometric and constant volume tests.