A microstructure-based procedure to simulate the effect of wetting-drying cycles on the soil water retention curve

Abstract

Analysing unsaturated soil response often requires the soil-water-retention-curve (SWRC). The SWRC depends upon the soil microstructure, which evolves with hydromechanical loading such as in-situ exposure to wetting-drying cycles. If in-situ response is of interest and studied in the laboratory, it is essential specimens have a structure representative of in-situ conditions. Simulating wetting-drying cycles in the laboratory is possible albeit time-consuming and a faster alternative procedure would be preferred, which is the focus of this paper. Mixtures of two soils were prepared in the laboratory by either: exposure to three simulated wetting-drying cycles, or one of two compaction approaches. The microstructure and drying-path SWRC of the specimens prepared with each method were measured. Most of the compacted specimens achieved similar pore size distributions to the cycled samples though the outcomes in terms of achieving a target SWRC, which was the objective of the study, are mixed. The SWRCs of most compacted samples had similar gravimetric water contents yet significantly higher saturation degree at every suction measured. This is explained by the compacted samples containing less macro pores than cycled samples. The compaction procedure, designed to produce specimens having a SWRC similar to that of cycled materials, seems promising but needs modification.