Résumé
Currently, Robinia pseudoacacia L. is distributed extensively across the Chinese Loess Plateau. Root exudates released by Robinia pseudoacacia L. are one of the mechanisms through which Robinia pseudoacacia L. affects soil properties. However, how root exudates influence the hydraulic properties of soil remains unclear, especially for fine-grained soils. This knowledge gap impedes a comprehensive understanding of the function of vegetation in wastewater treatment, ecological restoration, and seepage analysis. To investigate the effect and underlying mechanisms of the root exudates of Robinia pseudoacacia L. on the saturated hydraulic conductivity of loess (a fine-grained soil), the saturated hydraulic conductivity, bound water content, grain size distribution, and microstructure characteristics of loess treated with root exudates at varying concentrations were determined in this study through a series of tests. The results show that the mean saturated hydraulic conductivities of the loess specimens with root exudates are all lower than those without root exudates. This phenomenon can be attributed primarily to the capacity of root exudates to directly and indirectly increase the bound water content, leading to a decrease in the effective seepage channels of the loess. For loess with/without root exudates, the variation of saturated hydraulic conductivity over time can be divided into three stages: an initial constant stage, a rapid reduction stage, and a re-stabilization stage. This is primarily attributed to the migration of particles within a specified size range (7-30 μm) and pore-clogging in the specimens during the seepage process. A schematic diagram is proposed for the structural evolution of fine-grained soil with or without root exudates during long-term seepage.