Experimental Study On The Effect Of Entrapped Air On Quasi-saturated Soil Permeability

The progress of water entering into soil is called infiltration, it is an important problem of soil mechanics. In the progress of infiltration, a part of the volume of soil air is easily surrounded by water flow and closed in soil pores to form entrapped air. Thus the water flow is encumbered and the permeability is decreased, which results in great influence on infiltration. Therefore, the study on the content of entrapped air and its influencing factors as well as its influence on soil permeability is helpful to analysis soil infiltration capacity more comprehensively. These presses important guiding significance to the study of hydrology, farmland water conservancy and water environmentology.Based on one-dimensional ponded water infiltration in the laboratory, several works below is completed:1. The test model of one-dimensional ponded water infiltration is designed, and the curves of wetting front show that the step-like water content distribution exist at surface soil because of the entrapped air in soil. Further, the formation mechanism of entrapped air in soil pores is analyzed.2. The effects of dry density, initial water content and soil type on the volume of entrapped air are proposed, and the influencing mechanism of the three factors is discussed.3. Based on the results of the one-dimensional ponded water infiltration in the laboratory, the effects of dry density, initial water content and soil type on the infiltration rate are studied. The empirical formula for the permeability coefficient at the stable state of infiltration to the initial volume water content and the air saturation are fitted out. In addition, the reason of the effect of entrapped air on the permeability coefficient and the mechanism of the infiltration rate decreasing are anylysised.4. Using pressure membrane instrument, the soil-water characteristic curve of several soil samples are measured with the same soil indexes as the one-dimensional ponded water infiltration samples in the laboratory. Then, the results are fitted using the Fredlund&Xing model for the numerical simulation.5.The numerical simulating to one-dimensional ponded water infiltration is presented using the SEEP/W software, and the results showed that the numerical simulation results is mostly differ from the laboratory tests results, because the effect of the entrapped air on pore water pressure distribution and the permeability are not considered in SEEP/W.Thus, the influence of entrapped air on the water flow should be taken into considering in the numerical simulation.