Changes in Soil Permeability with Time and Mechanism of Pore Clogging

Abstract

The objective of this investigation is to consider the mechanism of pore clogging and clogging effects on the change in soil permeability with time.
Experimental results of soil permeability were classified into (i) increase in permeability with time (ii) decrease in permeability in the first stage (iii) constant in permeability. Authors investigated the mechanism of the decrease in permeability with time. Some clogging models of soil are divided into two types, one is the immediate clogging type of which clogging occurs by coarse particles in the pores, the other is the gradual clogging type by adhesion or sedimentation of fine particles to the inner walls. From the results of a microscopic observation of the soil sections and a comparison between calculated values of the clogging models and experimental ones, it was possible to suggest that pore clogging proceeded with the immediate clogging type due to soil suspension flow.
Little is known about the mechanism of immediate clogging due to soil suspension flow. The authors observed the decrease in the percolation volume of soil suspension through a porous medium against the increase in the volume concentration. Also, the changes in percolation volume per unit time were analyzed using the Buckingham-Reiner equation. The conclusion was that the rheological behavior of the soil suspension flow which caused one of immediate clogging was shown as follows.
R_j≤γ_0i (=2Lθ_i/ΔP_i)
where R_j is the pore radius, γ_0i the radius of plug flow, L the pore-length as the tube, θ_i the Bingham yield value, ΔP_i the difference of pressure. To prevent immediate clogging due to soil suspension flow, the radius of plug flow should be at least less than that of the pores.