Influence of microstructure on drying- and wetting-characteristics of fine-grained soils

ABSTRACT

The importance of soil water retention characteristics (SWRCs) for understanding behaviour of soil in its unsaturated state has been acknowledged in recent years. However, the hysteresis associated with SWRCs poses difficulties in relating the water retention characteristics with unsaturated soil properties. During wetting and drying cycles, soil, depending on its properties, undergoes microstructural changes (namely mainly changes in pore sizes and their distribution) and these changes would affect the hysteresis. However, few studies have attempted to quantify or demonstrate this aspect. This study attempts to relate the soil microstructure changes (quantified by dominant pore diameter, d_d) with the hysteresis associated with SWRCs (quantified by the slope of suction hysteresis, S_ψh), by employing mercury intrusion porosimetry, MIP, for obtaining the pore size characteristics at initial slurried stage, end of drying cycle and end of wetting cycle for different soils. Efforts are also made to understand the influence of soil-specific parameters on pore size characteristics. The results indicate that S_ψh and soil parameters such as clay content, specific surface area, cation exchange capacity and linear shrinkage are inversely proportional to d_d in air dry state. Further, the study presents the quantification of differential volume changes during drying and wetting processes for different soils.

KEYWORDS:

• Soil microstructure
• mercury intrusion porosimetry
• hysteresis
• soil water retention characteristics
• drying- and wetting-paths
• fine-grained soils

Acknowledgements

The authors extend sincere thanks to Professor Alessandro Tarantino and Ms. Mara Knapp at Department of Civil and Environmental Engineering and staff at Department of Mechanical and Aerospace Engineering at University of Strathclyde, Glasgow, Scotland for facilitating the MIP tests on the samples. The authors also extend thanks to Dr. Bruna C.F.L.L for her support in fitting MIP data with modified van Genuchten bimodal equation.

Disclosure statement

No potential conflict of interest was reported by the authors.