Abstract:  The mixing of sludge and sandy soil is a way to improve desertified soil. Understanding the pattern of water infiltration and redistribution in the composite soil would facilitate project improvement. To ensure the applicability of simulation software in practical engineering, we analyzed the pattern of water infiltration and redistribution of a mixture of sludge and sand with a 1∶4proportion under simulated rainfall process. The experimental process was simulated by using Hydrus-1D soil moisture simulation software. The simulated data were compared with the measured data to verify the applicability of Hydrus-1D software in simulating sediment composite soil water infiltration to select a suitable model. The results showed that the Hydrus-1D software can predict water characteristic curve of composite soil. Basic soil property parameters were obtained, including residual water content (θ_r), saturated water content (θ_s), air intake value reciprocal (α), pore size distribution index (n), and hydraulic conductivity (K_S). In the whole process of water infiltration simulation, water content of sand soil and composite soil graduallyincreased to a stable status close to but not equal to saturated water content. In the simulation test of water infiltration within 0-30 minutes, the difference between the measured curve and the simulated curve was not significant. After 60 minutes, the difference between the measured curve and the simulated curve in the simulation test of water redistribution in each soil layer was large. These results indicate that the software can simulate water infiltration, but not water redistribution.

Key words: water redistribution, Hydrus-1D, simulation applicability, characteristic curve, water content.