An Experimental Investigation of Non-Darcy Flow in Granular Porous Materials

Use of large grained gravel is increasing in hydraulic structures due to their specific features as regards filtration، canal covers، stilling basins، rockfill dams، etc. Flow behavior in high porosity media and as well in rockfill dams is very complex due to the existence of large pore size and consequently turbulence in the flow. Given the importance of flow within the rockfill materials، an investigation of the characteristics of this type of flow is indispensable. Considering the widespread use of large grained materials in civil projects، scrutinizing the flow properties in these materials and obtaining their hydraulic parameters is important as for non-Darcy flow studies. In order to study the flow behavior in grained materials، a constant-head permeameter was designed built. Experiments were carried out on three types of gravel grains with average diameters of 8. 69، 13. 08، and 16. 62 mm. During the course of experiments، the outlet discharge، upstream and downstream heads as well as a measurement of the pressure drop (difference between water levels in upstream and downstream tanks)، were recorded and their characteristics studied. The laboratory results indicate that the relationship between flow velocity and gradient is non-linear، following non-Darcy’s law. The evaluation of results using goodness of fit criteria and their comparison with Kadlec and Knight (1996) and as well Ergun (1952) relations show that the Kadlec and Knight (1996) relation is of a higher reliability than latter. Variation of Reynolds number versus friction factor shows that the more the diameter of materials، the lower the abrasion factor and the higher the Reynolds number. The friction factor in higher Reynolds numbers decreases so that it is independent of the grain diameter and of Reynolds'' number. The low pressure equations and relations obtained in this study can be used for calculation of water surface profile through dams and rock drains.