Abstract
It is known, concerning with infiltration into fine-over coarse layered soils, that water pressure at the interlayer plane increases rapidly when wetting front arrives at the plane and decreases after the occurrence of water penetration into the sublayer. This fact suggests that water entry threshold plays an important role in the occurrence and persistence of fingering flow. However, clear characterization of water entry threshold has not been given with relation to fingering phenomena, yet. Process of water penetration into packed glass beads with average diameter of 0.4mm was investigated. First, we measured the values of water entry threshold for initially dry and wet conditions by changing supply water pressure. Next, we measured infiltration flux under constant supply water pressure which was lower than the value obtained by the first measurement. In the first measurement, the value obtained for initially wet glass beads was lower than that for initially dry condition. For initially dry glass beads, we obtained the result that there was a discontinuous point of infiltration flux with the increase of supply water pressure. Therefore, the value of water pressure obtained by increasing supply water pressure could be regarded as a water entry threshold. On the other hand, obtained value for initially wet condition was not regarded as a water entry threshold because of continuous increase of infiltration flux. The values of the water entry threshold were discussed on the basis of the water characteristic curve for wetting process of the packed glass beads.
