Changes in clay structure and behaviour due to wetting and drying

A synthesis is presented concerning the mechanisms associated with clay structure and behavioural changes during wetting and drying. Generic units forming soil structure are identified as soil particles, particle associations and aggregations and particle clusters. It is evident that the clay structure and behavioural changes are controlled primarily by the changes in the pore size distribution. For young soils, the growth and rearrangement of particles and particle aggregation will produce a dense and stiffer structure during drying. For heavily overconsolidated soils, initially denser structures can regenerate to produce relatively loose structures. During drying, the frequency of macropores increases, whereas during wetting, the majority of the macropores close and transform into intercluster and intracluster pores. The development and the response of cracks are dependent on the restraint conditions placed on the soil and the initial stress state of the soil. The changes in pore system as well as the associated soil properties appear to stabilise as the number of wet/dry cycles increases.