Influence of soil layer structure on unsaturated capillary water and salt transport

The discontinuity of pore structure and hydraulic properties between layered soils has a significant influence on the transportation of water and salt. Based on the field investigation, the laboratory soil column tests of two soil layer binary structure combinations (loess-sandy silt and loess-silty clay) were designed. Through the model tests, the influence of soil layer structure on capillary water distribution and salt accumulation under different groundwater supply conditions was discussed. The test results show that under the condition of capillary water supply, the upper-fine and lower-coarse soil layer structure composed of loess-sandy silt is beneficial to capillary water and salt transportation. After 60 days of evaporation, the surface content of the upper-fine and lower-coarse soil column is twice of the upper-coarse and lower-fine soil column. Under the condition of no capillary water supply, the total amount and rate of upward migration of water and salt in the sandy silt layer is greater than that of the silty clay layer, and finally the ion content of each of the overlying soil layer in the upper-fine and lower-coarse soil column is greater than the upper-coarse and lower-fine soil column. The research results provide experimental reference for the prevention of saline soil disease in layered soil areas.