Rate of capillary rise in a column of uniform sized spheres

Capillary rise is an important phenomenon in the vadose zone. Capillary rise technique has also been applied to determine the soil-water characteristic curves of porous media. The capillary height is commonly calculated using Kelvin's equation. The rate of capillary rise is less often investigated but is important if the capillary rise technique is used to determine the soil-water characteristic curve of a porous medium as it governs the duration of the experiment. The Lucas-Washburn's equation is often used to estimate the rate of capillary rise. A similar equation for rate of capillary rise was presented by Terzaghi in 1943. However, some discrepancies were found between Lucas-Washburn's equation and experimental observations. The objective of this paper is to investigate the discrepancies between Lucas- Washburn's equation and experimental observations. A series of tests using columns of uniform sized spheres was conducted. The tortuosity parameter in the Lucas-Washburn's equation requires modifications in order to obtain a good agreement with the experimental data. The form of the tortuosity parameter requires further investigation.