Cyclic swelling of clays

Abstract

Changes in free swelling and swelling pressure of different types of clays in response to varying cycles of wetting and drying have been studied. It can be shown that cyclic tests lead to a gradual destruction of the durable contacts in the clay structure and their transformation into less durable ones. At the same time, a reconstruction of the structure of the clays takes place, manifested by the destruction of large micro-aggregates and by disorientation of structural elements. All these phenomena result in great swelling with increase in the number of wetting cycles. Between cycles 3 and 20 the expansibility is at its maximum and may be 1.3–10 times as much as that after one wetting cycle. Cyclic swelling leads to an overall equilibrium in the system, when the internal energy of the clay is minimal and the bound water content is at its maximum. Clay in this state exhibits its maximum moisture uptake ( W′ s), the meaning of which is of thermodynamic character and depends neither on the initial soil density and moisture, nor on the scheme of cyclic tests adopted.