Investigation of Non-Darcy Flow for Fine Grained Materials

Research efforts have been done to determine the limit of validity of Darcy’s Law in various fields of engineering where viscous conditions of flow are likely exceeded. In geotechnical and geological engineering, the application of centrifuge modeling for studying flow through porous materials is complex because the seepage velocity scales proportionally to centrifuge gravity, resulting in greater potential for exceeding the limit of viscous flow. This limit is usually estimated based on Forchheimer’s Law and the concept of critical Reynolds number, R_critic, but its interpretation remains ambiguous. This study provides new insights and establishes a connection between different theoretical approaches available in the literature. Centrifuge permeability tests were conducted at different gravitational levels for different materials. Effects of the characteristics of the porous media and centrifuge acceleration on the flow behavior were evaluated. Results show that parameters of Forchheimer’s Law remain constant regardless of the centrifuge acceleration. Values of R_critic were obtained in a range from 0.2 to 11 depending on the characteristics of material. The interpretation of the limit of validity of Darcy’s Law was analyzed based on different definitions of Reynolds number and the Forchheimer number, and critical velocities of flow and hydraulic gradients were estimated.