Evolution of soil-water and shrinkage characteristics of an expansive clay during freeze-thaw and drying-wetting cycles

Abstract

This paper investigates the evolution of the soil-water characteristic curve (moisture content-suction relationships, SWCC), soil shrinkage characteristic curve (moisture content-void ratio relationships, SSCC) and microstructure of a compacted expansive clay during drying-wetting (DW) cycles and closed-system freeze-thaw (FT) cycles. Experimental results reveal that FT and DW cycles significantly change the clay's macropore system by destructing the compaction-induced macropores but have little impact on the micropore system. FT cycles induce invisible microcracks and DW cycles result in visible macrocracks, both of which (i) significantly reduced the clay's water retention capacity in the low suction range and volumetric shrinkage from saturated condition to oven-dryness, (ii) introduce structural shrinkage stage to the SSCC and (iii) have no impact on the shrinkage and plastic limits of the SSCC. The slope of the SSCC in the normal and residual shrinkage stages reduces after FT cycles due to the development of microcracks but is less affected by DW cycles. The moisture content-void ratio-suction relationships obtained from specimens with different FT and DW histories are likely distributed on a unique surface and this surface was reasonably described by a model proposed in this study using only one set of parameters. Studies in this paper are useful for advancing the understanding of the influences of environmental factors on the hydromechanical behaviour of expansive clays.