Relationship between soil structure and water retention properties in a residual compacted soil

• The hydro-microstructural behavior of a compacted residual tropical soil is presented.
• Relation between hydraulic and pore size distribution is shown by results.
• The importance of volumetric changes during determination of WRC
• To high suction values, adsorption is more important than capillary effect.
• Simple techniques can be used to take into account the adsorption effects.

Soil structure, especially the soil pore size distribution, is a fundamental property that describes the hydro-mechanical behavior of soils. The volume change behavior, shear strength, water retention capacity and hydraulic conductivity of soil are controlled by the pore size distribution. However, research on soil structure has been limited due to the associated expenses and specialized instruments, such as environmental scanning electron microscopes and mercury intrusion porosimeters (MIPs). In this study, the relationship between the soil water retention curve (WRC) along a drying path and the pore size distribution obtained through an MIP method was reviewed. The WRC for a compacted tropical soil was converted into a soil air injection curve and then used to estimate the pore size density (PSD) function. Relative to the data collected from MIP methods, the results showed an acceptable prediction of the PSD function based on a soil air injection curve. Finally, a series of adjustments to the air injection curve were performed to improve the accuracy of the PSD prediction based on the water retention curve.