Influence of Particle Size Distribution and Microstructure on Water Retention and Infiltration in Lateritic Soils

Lateritic soils are widely distributed across tropical and subtropical regions, particularly in the Southern Hemisphere. Their diverse microstructures and granulometries influence water retention and infiltration. Pore connectivity influences moisture distribution and drainage efficiency, while particle microaggregation can modify the conventional relationships between granulometry and hydraulic behavior. This study evaluates the influence of particle size distribution and microstructure on water retention and infiltration in lateritic soils. Undisturbed soil samples were collected at a 2 m depth in Londrina, Paraná, Brazil, and analyzed using sieving, sedimentation, and adapted methodologies to assess fine particle microaggregation. Scanning Electron Microscopy (SEM) characterized structural features, while results were compared with Soil-Water Characteristic Curves (SWCC) and hydraulic conductivity data. Particle size analysis classified the soils as silty clay (CM), sandy silt (MS), and silty fine sand (SM), confirming microaggregates in the silt and clay fractions. SEM images highlighted the role of microstructure in water retention and infiltration. Higher saturated hydraulic conductivity (ks) in the first meter suggests increased water retention in intra-aggregate pores, whereas occluded voids at 2 m depth reduced connectivity, lowering retention. These findings enhance the understanding of the relationship between soil structure and hydraulic behavior, providing important insights for the design of infiltration systems in lateritic regions.