Anomalies in Capillary Intake as Explained by Capillary Rise Experiments

Abstract

AbstractIn an earlier study of soil structure, an attempt was made to utilize as a soil structure index, the proportionality constant in the square‐root‐of‐time equation of horizontal capillary flow. In the present paper, anomalous variations of this constant—the capillary absorption coefficient—are considered in greater detail.As a starting point, the movement of the meniscus in a single round capillary tube was assumed amenable to treatment on the basis of Poiseuille's law. Using data from the literature, it was found that there is validity in the Poiseuille analysis. However, quantitiative agreement with the experiments depended somewhat on the conductivity K of the capillary tube.The Poiseuille analysis was then utilized in a theoretical treatment of the capillary absorption coefficient, assuming an idealized soil model consisting of parallel, non‐interconnected capillary tubes. From the intersection behavior of capillary rise curves, it was found possible to predict within limits the behavior of the capillary absorption coefficient as affected by changes in pore radius, surface tension, wetting angle, and viscosity.Experimental curves of capillary rise versus time were then obtained for the soils of the previous structure study for which values of capillary absorption coefficient had already been measured. The observed behavior of the coefficient, especially when a large variation was induced in it by a given structure treatment, was found to be consistent with the behavior predicted on the basis of capillary rise curves.The favorable qualitative comparisons of the capillary tube theory with the experimental data for the soils tested, suggest that the theory can be refined for determining more simply the now difficulty determinable soil physical property—the wetting angle.