Simple Model for the Estimation of the Bimodal SWCC of Highly Weathered Tropical Soils

The soil water characteristic curve (SWCC) of highly weathered tropical (i.e., lateritic) soils is often bimodal, with distinct drainage suction ranges associated with the macrostructure and the microstructure. This bimodal behavior is commonly attributed to fine particle aggregations that affect soil fabric and pore-size distribution. This paper presents a simple model to predict the drying SWCC of bimodal lateritic soils based on the SWCC parameters from the Gitirana–Fredlund fitting equation. The model was developed based on nonlinear regression analyses and using a soil database consisting of 15 remolded and 25 undisturbed soils. The database contains routine geotechnical data, including index properties, grain-size distribution (GSD) curves, and drying SWCCs. The findings suggest that porosity, liquid limit, relative aggregation, and GSD parameters have significant physical relationships with the SWCC, allowing a relatively accurate estimation of the SWCC parameters. The R2 values obtained for the SWCCs present in the database were 0.89 for remolded soils and 0.92 for undisturbed materials. The liquid limit was found to be more strongly associated with SWCC parameters describing water adsorption, whereas the other variables are strongly related to capillarity storage parameters.