Abstract:

A part of air in soil is easily surrounded by water flow and entrapped in the pores of unsaturated soil in the infiltration progress. The entrapped air is neither continuous with each other nor with the external atmosphere. Thus the water flow is encumbered and the permeability is decreased, which results in great influence on infiltration. Based on the previous research and the results of one-dimensional ponded water infiltration in the laboratory, a preliminary research on the formation of entrapped air and its influence mechanism on infiltration are conducted. This research is important to understand the water-air two phases flow in unsaturated soil. The test results show that the entrapped air is found in all ponded water infiltration tests, which is related to soil type, dry density, and initial water content. The entrapped air occupies more void in larger dry density sample and has greater influence on water flow. Under the same dry density condition, the entrapped air in clay soil affects infiltration greater than that in sand soil. The less the initial water content is, the greater the entrapped air volume is. At the steady state of infiltration, the water content is about 80 % to the saturated water content.

Key words: entrapped air, one-dimensional ponded water infiltration, influence mechanism