Research on the vertical nonlinear Darcy seepage characteristics of coarse upper and fine lower saturated sand

The investigation of seepage characteristics in double-layer sand contributes to a deeper comprehension of the seepage mechanism in porous media, as well as enhancing the accuracy of porous media seepage calculations. By employing a configuration consisting of six variations of upper coarse and lower fine double-layer sand, alterations in flow rate and hydraulic gradient were achieved by manipulating liquid level heights. This analysis examines the correlation between hydraulic gradient, flow velocity and hydraulic conductivity. The research reveals that the double-layer sand exhibits Darcy non-linear flow, despite having a very low Reynolds number (Re), and emphasises the influence of particle size in the lower sand layer on hydraulic gradient and hydraulic conductivity. Moreover, the enhanced Ergun formula was utilised to evaluate viscous resistance and local resistance during the flow process, while also presenting an empirical formula for interface resistance derived from experimental data.