Mechanics of Unsaturated Soils: from Equilibrium to Transient Conditions: Fid-Bau Portal

Mechanics of Unsaturated Soils: from Equilibrium to Transient Conditions

Nikooee, E. / Hassanizadeh, S. Majid / Habibagahi, G.

Since early stages of the unsaturated soil mechanics, a long-lasting debate has started on the choice of suitable stress state variables; this has given birth to various frameworks. A central question for the debates was the effective stress formulation for unsaturated soils and efficacy of effective stress approaches to model mechanical behavior of such soils. One important ingredient of all formulations is matric suction (capillary pressure), whether considered as a part of a single effective stress or simply as a separate stress state variable. Therefore, a relationship between matric suction and saturation will always be an inevitable part of any hydro-mechanical model in unsaturated soil mechanics. One should note that we usually measure this relationship at equilibrium state. In geotechnical engineering practice, soil water retention curves which express this dependency are usually measured under quasi-static conditions. Thus, the whole theory of modern unsaturated soil mechanics has been built around soil water retention curves at equilibrium state, which is not the case in many practical situations (e.g., there is no equilibrium during rainfall-induced landslides). It is, therefore, necessary to discuss and disclose the importance of dynamic soil water retention curves and their influence on unsaturated soil mechanics. In this paper, after a brief review of recent researches/advances on nonequilibrium theories of two-phase flow, major consequences of these advancements for unsaturated soil mechanics and potential research directions for theoretical and experimental future works are presented.