Statistics-based method for determination of drag coefficient for nonlinear porous flow in calcareous sand soil

Generally, drag force applied by soil particles to seeping pore water is described as a type of body force in the form of hydraulic gradient I. For steady porous flow, the hydraulic gradient was widely formulated by the Forchheimer equation, containing two Forchheimer drag coefficients a and b. In this study, a simple and novel experimental device is designated to study the seepage characteristics of pore water in soils. Taking the calcareous sand soil coming from the South China Sea (SCS) as a typical porous medium, three parallel tests of seepage flow are performed. Based on the experimental data of apparent speed u of pore water and corresponding hydraulic gradient I, a statistic-based methodology is proposed to determine drag coefficients a, b of SCS calcareous sand soil. The priority of the proposed methodology is that the statistic distribution of measured parameters can be clearly observed through a small number of tests. Comparative study shows that the drag coefficient a and b of SCS calcareous sand soil determined by the statistic-based method proposed in this study can perfectly describe the corresponding experimental data of u-I relationship. It is indicated that the proposed statistics-based methodology to determine drag coefficient of soil is reliable and feasible.