Longitudinal Dispersivity of Partially Saturated Sand Packed into Air Suck Column

Abstract

Dispersion coefficient has been estimated from the best fitting of one-dimensional convection-dispersion model with laboratory experiments in transport of aqueous constituent through sand column. Suction is applied to the bottom to get rid of the end effect and to keep constant in water saturation throughout the column. The Toyoura sand was packed and sodium chloride solution was supplied with steady state flow condition. The experimental results indicated that the dispersion coefficient increases dependently on the decrease of water saturation and a linear relationship exists between dispersion coefficient and average pore water velocity when dispersion coefficient is evaluated at the same water content. The study highlights the linear increase of dispersivity, which is defined by the dispersion coefficient divided by the average pore water velocity, as water saturation decreasing. Physical meaning of this tendency is considered by the shape of breakthrough curve describing concentration distribution at solute front.