Influences of drying-wetting-freeze-thaw cycles on soil-water and shrinkage characteristics of expansive soil

The effects of freeze-thaw (FT), drying-wetting (DW) and alternative drying-wetting-freeze-thaw (DWFT) cycles on the micro-structure, soil-water characteristic curve (SWCC) and soil shrinkage characteristic curve (SSCC) of a compacted expansive soil are investigated. The experimental results show that the three investigated cyclic treatments significantly change the macro-pore system of soil. The macro-pores formed during compaction disappear during DW cycles while visible cracks are introduced. FT cycles induce invisible micro-cracks, and macro- and micro-cracks are both discovered in DWFT specimens. Macro- and micro-cracks significantly reduce the water retention capacity of soil in the low suction range and the amount of shrinkage from saturated condition to oven dryness. They have no influences on the SWCC in the high suction range and the shrinkage limit and plastic limit of soil. The slope of the SSCC at the proportional and residual shrinkage stages decreases after FT and DWFT cycles but remains constant after DW cycles. The relationships among moisture content, void ratio and suction of soil after different FT, DW and DWFT cycles are distributed on a unique surface which can be reasonably described by the proposed modified model. This study is useful for understanding the hydro-mechanical behavior of expansive soil under the influences of environmental factors.