For many years there has been interest in differences in the behaviour of soils during drying and re-wetting. The difference is referred to as hysteresis, and workers in the field of unsaturated soil mechanics as early as Croney et al. (1952) have drawn attention to the necessity of knowing whether a soil is on a drying or a wetting path in order to predict its future behaviour. The paper will draw parallels between consolidation relationships in saturated soils where pore pressure is positive or zero and suction water content curves (SWCC) for unsaturated soils where pore pressure is negative. The reader will be reminded that hysteresis between compression and swelling curves in saturated soils only occurs if stresses are changing from a normally consolidated to an overconsolidated state. In soils subjected to drying and re-wetting, the analogue to this is that hysteresis is only significant between the SWCC for the first drying of soil and that for the first re-wetting. Subsequent re-drying and re-wetting paths very closely follow that for first re-wetting. The consequence of this is that seasonal wetting and drying of natural soil strata takes place with negligible hysteresis between wetting and drying paths. These statements will be supported by experimental data both from the established soil mechanics literature and tests by the author.
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