Abstract
The swell-shrinkage behavior of expansive clays was investigated in four soils of different plasticity cyclic swelling. To simulate drying temperatures typical of site conditions, two shrinkage schemes were adopted, partial and full shrinkage. After each cycle, the expansive characteristics of the soils were assessed. Furthermore, the physical and microstructural changes due to cyclic swelling were also studied, respectively, through an ultra-sonic investigation and scanning electron microscope observations. The results showed that cyclic swelling and shrinkage has a marked influence on the expansive behavior of clays. Generally speaking, a decrease in the swelling ability of the clays, corresponding to a reduced water absorption capability, was observed when the soils were alternately wetted and partially shrunk. On the other hand, an increase in the swelling potential was noted when the soils were fully shrunk. In either case, equilibrium can be attained after several cycles. As the number of cycles increase, further destruction of large aggregates and disorientation of structural elements takes place. Approximately after the fifth cycle, the fabric becomes almost disoriented, consequently further changes in expansibility disappear. The scanning electron microscope analysis showed that for partial shrinkage the structural elements exist mainly as edge to face contacts with a tendency to form a turbulent flocculated system while a horizontal clay particle orientation was observed when the specimens were cyclicly wetted the fully shrunk. In parallel, the ultrasonic wave transmission velocity increased with the number of cycles in the first case, and decreased when transmitted through a fully shrunk soil sample.