Estimating family of soil–water characteristic curves for sandy soils from unimodal grain size distribution and void ratio

Soil-water characteristic curves (SWCCs) are a family of water content values versus soil suction, illustrating the hysteresis in natural soil. The accurate and efficient estimation of SWCCs is indispensable in geotechnical engineering and hydrology. This paper aims to develop a comprehensive model for accurately estimating the family of SWCCs for sandy soils using their unimodal grain size distribution (GSD). First, an improved model is developed by combining the physical-based MV model with statistical estimation to predict the initial drying SWCC. This model explicitly quantified the effects of soil uniformity and residual water content on estimated SWCC based on GSD. Second, the model is further developed to predict the main wetting curve from the estimated drying curve by introducing residual air content, contact angle hysteresis, and “ink bottle” effects. The drying and wetting scanning curves are predicted for any given transition point. Then, the model’s performance is evaluated through comparison with experimental data from various sandy soils, cross-validation, sensitivity analysis, and uncertainty quantification. Results show that the model stands out for its superior accuracy and convenience compared to classical models. It provides reliable predictions of the entire family of SWCCs for a wide range of sandy soils, from gravelly to clayey sand. Finally, the potential application in other fields and limitations of the model are discussed. The model also demonstrates the potential to be extended to various soil types, including gap-graded soils, fine-grained soils, and soils with organic matter.