Clay Upward Movement in Sand Columns under Partially Saturated Conditions

Almost all the studies on clay movement have been focused on downward movement rather than upward except one study that focused on upward movement. Therefore, this study was conducted to assess the impact of different clay suspension concentrations on the upward movement of clay particles. In this experiment, 24 transparent glass tubes with dimensions of 50-cm height and 3.7-cm internal diameter were packed with quartz sand. All of the sand columns were installed vertically in plastic containers. Two experiments were conducted: one represented a continuous wetting (CW) system and the other represented a wetting and drying system (WD). Each experiment had 12 sand columns distributed in four groups with three replicates. A stock of clay suspension was prepared from a 3-kg clayey textured soil sample obtained from a Vertisol in the Delta of the Nile River. Four clay suspension concentrations (2, 4, 6, and 8 g L-1) were prepared and provided to the sand columns from the bottom by filling the plastic containers to a 13-cm height. Each group of plastic containers was filled with one of the four clay suspensions (2, 4, 6, and 8 g L-1). The results revealed that clay particles moved 43 cm upward in all of the clay suspension concentrations and precipitated on the walls of the pores and at the capillary fringe (air-water interface). Clay contents in all of the layers in the WD cycles were higher than those in the CW system. The middle layers of the sand columns showed low clay content compared with the lower and upper layers.