Characterization and quantitative evaluation of preferential infiltration in loess, based on a soil column field test

Preferential infiltration occurs widely in loess deposits and has a major impact on water movement and redistribution. However, preferential infiltration is a complex process, and previous research has focused principally on its qualitative description. Few studies have carried out infiltration tests to assess preferential infiltration in loess. In this study we conducted five soil column infiltration field tests in the Heifangtai area of Gansu Province, China, to explore preferential infiltration processes and the characteristics of loess. Based on the test data, the preferential infiltration is qualitatively assessed, and a quantitative calculation method for the preferential infiltration of loess with vertical cracks is proposed. The following conclusions were drawn: 1) The relationship between the infiltration rate of loess and the reciprocal of wetting front depth is a positive linear relationship under homogeneous infiltration, but non-linear under preferential infiltration. 2) The degree of preferential infiltration can be determined based on the distance of data points to the infiltration rate-wetting front propagation velocity gradient under homogeneous infiltration. 3) Based on the principle of similarity of infiltration of adjacent soil, we calculate that the preferential infiltration rate of closed cracks is two to three orders of magnitude greater that the homogeneous infiltration rate, and that the contribution of stable preferential infiltration to the total infiltration is about 20%. Quantitative evaluations of preferential infiltration are helpful in calculating slope seepage, evaluating slope stability, and researching landslide initiation mechanisms.