Effective Stresses in Multiphasic Porous Media: A thermodynamic investigation of a fully non-linear model with compressible and incompressible constituents

In literature, it is often said that the Principle of Effective Stresses'' has been introduced in soil mechanics by Karl von Terzaghi in 1925 in his famous book Erdbaumechanik auf bodenphysikalischer Grundlage'' stating that the total stress acting in a soil body can be split into an effective stress and the pore-water pressure. While the effective stress is coupled to the soil deformation, the pore-water pressure, in particular its gradient, governs the pore-fluid flow usually following Darcy's law. In earlier days, Terzaghi's principle has been taken as a constitutive equation not only under fully but also under partially saturated conditions, although doubts came up with regard to its overall validity. Starting with a short historical review, the present article aims at explaining the effective-stress principle from a general point of view on the basis of the Theory of Porous Media and provides an elaborated example for both unsaturated and saturated soil conditions by consideration of compressible and incompressible solid and pore-fluid materials. Based on this approach, it will be proven that Terzaghi's basic assumption of the effective-stress principle is valid, except for materially compressible porous solids. (c) 2017 Elsevier Ltd. All rights reserved.