A PHYSICALLY BASED MODEL FOR SURFACE SEALING OF SOIL

A physically based model describing the mechanism of surface seal formation of soil from a suspension of soil in flowing water was formulated on the basis of the principle of conservation of mass and Darcy's equation for the flow of water through a layered soil column. The model shows that, for sufficiently large times, the flux density of the filtrate is proportional to the inverse square root of time. The proportionality constant is a function of the saturated hydraulic conductivity and bulk density of the seal, and the concentration of the suspension. The components of the proportionality constant suggest that the constant could be used as an index of structural stability of soil. For the three suspensions used in testing the validity of the model, log-log plots of the flux densities of the filtrates and time showed linear relationships with slopes approximately equal to -0.5, as predicted by theory. However, using calculated components of the model to predict flux densities of the filtrates failed to show agreement for two out of the three suspensions used. This was attributed to some over-simplified assumptions used in the model, such as constant concentration and no sedimentation effects during the filtering process. It is suggested that incorporation of a time-dependent concentration and sedimentation factors could perhaps improve the efficacy of the model.