Mechanical fundamentals of seepage force concept and its generalization

The seepage force is still one of the most fundamental and controversial concepts in soil mechanics. Based on the literature review, the compatibility between the definition of hydraulic gradient and the mathematical description of Darcy’s law is discussed first, followed by proposing a compatible form of hydraulic gradient definition in the conventional expression for seepage force. By integrating the body force, the general effective stress principle and the total seepage potential equation into the Biot’s consolidation theory, a strict definition of the general seepage force is obtained for various porous media including soils. The general seepage force proposed herein is the dot product of the general effective stress tensor and the total seepage potential gradient, which differs from conventional explanations of seepage force mechanism. Within the scope of Terzaghi's effective stress principle, the general seepage force is reduced to the form of total seepage potential gradient. Other related mechanical properties of seepage force are investigated as well as a further modified formulation for the general seepage force containing seepage velocity. The conclusions may afford profound insight into the concept of seepage force in geotechnical practice.