special case is the downward displacement of the foundation due to the drying of underlying
wet clays, which will be discussed in Chap. 9. Often this downward displacement of the foundation
caused by the desiccation of clays is referred to as settlement. But upon the introduction of moisture,
such as during the rainy season, the desiccated clay will swell and the downward displacement will
be reversed. The foundation could even heave more than it initially settled. When dealing with
expansive clays, it is best to consider the downward displacement of the foundation as part of the
cyclic heave and shrinkage of expansive soil and not permanent settlement.