Reversible and irreversible deformations of expansive clays

The aim of this study was to investigate the size effect of reversible and irreversible components of volume change behaviour of highly expansive and moderately expansive soils experimentally. The soil deformations of small-, large- and extra-large-scale samples were measured during wetting and drying cycles. Accurate dial gauges were used for measuring vertical deformation, and digital image correlation techniques were adopted for measuring horizontal desiccation cracks using a microcrack measuring device. Wetting and drying cycles that rely on seasonal moisture content variations in the subsoils were performed on an extra-large field model of a highly expansive soil. Results were compared with those of standard swelling tests to estimate vertical swelling and shrinkage-induced soil deformations that are expected in practice under public infrastructures. The field model, which represents reconstituted soil samples, presented a free swelling of 3·61% in the first cycle. In the second cycle, reversible free swelling increased by 7·68% over the first cycle given the irreversible components of shrinkage caused by lateral desiccation cracks. Irreversible deformations were observed during the drying processes through a network of microcracks and macrocracks. The reversible and irreversible deformations during the first drying process were 45·7% and 54·3%, respectively.