Experimental Investigation of Water Infiltration Law in Loess with Black Locust (Robinia pseudoacacia) Roots

Physical model experiments are increasingly applied in the study of the water infiltration law in loess with roots. In the past, due to differences in study objects and the limitations of measuring techniques, the infiltration law in loess with roots is rarely evaluated by using appropriate indoor physical model experimental data. In order to investigate the law of water infiltration in loess with roots, we designed a new soil column experimental device that can automatically collect data and images. By comparing the soil column experiment data of loess, we analyzed variables in root contents (the ratio of root mass to dry soil mass) and root types. Roots with diameters of 0-2 mm, 2-5 mm, and 5-10 mm are defined as type I, type II, and type III, respectively. It was found that the water infiltration rate, water-holding capacity, and saturated permeability coefficient increase with the increase in root content. In loess containing different root types, the root types were found to improve the rate of water infiltration, water-holding capacity, and saturated permeability coefficient in the soil. The root types were ranked in descending order in terms of their impact: root type II had the highest improvement, followed by root type III, and then root type I. The phenomenon of circumferential flow existed when water infiltrated loess with roots. Root content and root type would affect the radius of circumferential flow, infiltration path, and cross-section. When calculating the saturated permeability coefficient of loess with roots, ignoring the effect of circumferential flow would lead to a higher result.