WATER-MOVEMENT IN GLASS BEAD POROUS-MEDIA .2. EXPERIMENTS OF INFILTRATION AND FINGER FLOW

This paper presents experimental observations of infiltration and fing er flow in glass beads. In paper 1 (Lu et al., this issue), we showed that the total surface tensile force is much greater in initially wet profiles than in initially dry profiles. During capillary rise in glas s beads, the ''jump'' process takes place for an initially dry conditi on, whereas in an initially wet profile not only a jump process but a film thickening associated with film flow characterizes capillary rise . In this paper, infiltration experiments into initially dry glass bea ds show that the wetting front is relatively saturated and flat compar ed with the unsaturated and irregular wetting front into an initially wet profile. In the experiments of finger flow, photographs show that the tip of the finger is completely water saturated and that no partia lly saturated zones exist around the saturated tip. The fingers initia ted in a dry zone disappear when they reach an initially wet lower zon e even when the packing conditions of the glass beads are identical. H ence the criterion for instability when water is applied at a rate les s than the value of the saturated hydraulic conductivity does not appl y to an initially wet condition. When a fine layer of glass beads lies on a coarse layer that is initially dry, fingering will take place du ring infiltration and flow is unstable. If the coarse lower layer is i nitially wet, finger flow does not develop, and the flow remains stabl e. More investigations are required to ascertain threshold values of t he initial water content causing instability of water movement in poro us media.