The soil water retention curve (SWRC) strongly influences the hydro-mechanical properties of unsaturated soils. It plays a decisive role in geotechnical and geo-environmental applications in the vadose zone. This paper advances a novel framework to derive the water retention behavior of multimodal deformable soils based on the pore size distribution (PSD) measurements. The multiple effects of suction on the soil pore structure and total volume during SWRC tests are considered. The complete picture of soil microstructure is quantitatively described by the void ratio (for the pore volume) and a newly defined microstructural state parameter (for pore size distribution) from a probabilistic multimodal PSD model. Assuming a reversible microstructure evolution, a unique PSD surface for wetting and drying links the SWRC and PSD curves in the pore radius-suction-probability space. A closed-form water retention expression is obtained, facilitating the model's implementation in particle applications. The model is validated using the water retention data of four different soil types, showing a strong consistency between the measurement and the reproduced curve. The proposed method provides new insights into the pore structure evolution, the water retention behavior and the relationship between them for multimodal deformable soils.

Lateritic clay is often used as a construction material for roads in tropical and subtropical areas. However, these materials exhibit high compressibility, high rate of creep, and susceptibility to severe cracking due to swelling and shrinkage behavior. These traits are closely linked to its hydro-mechanical and deformation properties. In this study, firstly, a boundary line between the swelling and compression deformation zone was determined based on the results of wetting tests. This boundary line is crucial for identifying the specific deformation mechanisms observed in unsaturated lateritic clays under varying water conditions. Secondly, an analysis of the relationship between pore size distribution and the soil water retention curve (SWRC) were conducted. A simple bimodal SWRC model, using the normal distribution function, was proposed. Additionally, the strength characteristics of lateritic clay were investigated over a wide suction range. It was observed that the existing strength model significantly underestimated the tested values in the medium to high suction range. To address this, a segmented strength equation was introduced based on unsaturated effective stress analysis. This approach allows enables enhanced predictions of the strength properties of lateritic clay. Altogether, these findings have greatly contributed to a better understanding of the engineering properties of lateritic clay.