Comparison of air entry values from soil water retention and volumetric shrinkage characteristic curves

Abstract

The soil water retention curve (SWRC) is the relationship between the volumetric water content and the matric suction of an unsaturated soil. One key parameter of the SWRC is the air-entry value (AEV), which defines the minimum matric suction at which air starts to enter the largest pores in the soil as it desaturates. The volumetric water content at the AEV can also be identified from the evolution of the volumetric shrinkage characteristic curve (VSCC). The VSCC is the relationship between the void ratio and volumetric water content of an unsaturated soil as it dries towards the shrinkage limit. Fine-grained materials, such as dredged materials and mine tailings comprising clay minerals and natural clays, show a marked volume change with variation of the water content. In this study, the AEVs of three fine-grained materials (dredged material, red mud and kaolin) were measured from SWRCs and compared with the shrinkage limit values obtained from the corresponding VSCCs. The SWRC was measured by utilizing full-range polymer tensiometers. The polymer tensiometer is filled with polymer solution instead of water, diminishing the effect of soil salinity, and can measure the matric suction up to -1500 kPa. The SWRC and VSCC results were compared and discussed in terms of their applicability to providing an understanding of unsaturated soils that undergoing large volume change.