Effect of Muddy Water Characteristics on Infiltration Laws and Stratum Compactum Soil Particle Composition under Film Hole Irrigation

To investigate the impact of sediment on water infiltration and soil structure under muddy water irrigation conditions, indoor muddy water film hole infiltration experiments were conducted. Four different muddy water sediment concentrations (3%, 6%, 9%, 12%) and four typical sediment particle size distributions (which were quantified by the physical clay content with a particle size of less than 0.01 mm, d0.01: 9.13%, 16.46%, 27.34%, 44.02%) were employed to examine how muddy water properties affect infiltration law and the stratum compactum soil particle composition under film hole irrigation. The results showed that as the muddy water sediment concentration and physical clay content increased, the wetting front migration distance, cumulative infiltration amount, and soil water content gradually decreased simultaneously. The Kostiakov infiltration model effectively captured the changes in soil water infiltration during muddy water film hole irrigation, exhibiting a strong fit with a high coefficient of determination (R2 > 0.9). With higher muddy water sediment concentration, the deposition layer thickness increases within the same infiltration time. Conversely, higher physical clay content leads to a decrease in deposition layer thickness. The characteristics of the muddy water have a significant impact on the particle composition of the soil in the stratum compactum caused by film hole irrigation. The deposition layer has a lower relative content of fine soil particles compared to muddy water, but this content increases with higher muddy water sediment concentration and physical clay content. In the stranded layer soil, fine particles have a higher relative content than the original soil. Fine particle content increases notably with higher muddy water sediment concentration and physical clay content. The stranded layer soil particles exhibit a higher fractal dimension than the original soil, and as the infiltrated soil layer depth increases, the soil fractal dimension decreases until it matches the original soil. The fractal dimension increased with the increase in muddy water sediment concentration and physical clay content in muddy water irrigation conditions under the same soil layer depth. This research findings could serve as a theoretical foundation for understanding soil water movement under muddy water irrigation conditions.