Modeling the bimodal SWCC of highly weathered tropical soils using grain-size information

Abstract

The soil-water characteristic curve (SWCC) of highly weathered tropical soils is often bimodal, presenting two main slopes that are strongly related to the macro and micropores. The bimodal SWCC behavior is commonly attributed to fine particle aggregations that affect soil fabric and its pore-size distribution. In this paper, the relationship between basic soil properties (e.g., the Atterberg limits and the grain-size distribution) and the bimodal SWCCs are investigated using a database comprised of 40 different remolded and undisturbed soils. The proposed modeling framework is based on the relationship between the pore-size and the grain-size distributions, using a newly proposed soil property called the β-function. The findings suggest that microporosity has a strong relationship with the liquid limit whereas the total porosity varies mainly as a function of the macrostructure. The grain-size distribution curves under aggregated and disaggregated conditions offer key information on the degree of aggregation and, consequently, on the retention properties of macro and micropores. Several basic soil properties are found to be related to the desaturation zones of the micro and macropores, including the coefficient of uniformity of the fine particle range and the degree of particle aggregation. The developed model offers reasonable estimations for suctions up to approximately 20,000 kPa, with performance exceeding R² values of 0.80.