Volume change behavior

The volume of the soils will either decrease or increase upon wetting. The volume of unsaturated expansive soils will increase, while volume will decrease (collapse) for loessial soils upon wetting under a constant applied stress. The following sub-sections describe the characteristics of these soils due to changes in the moisture content.

Naturally existing active clays

Active clays or the expansive clays are the clays that experience usually large swelling strains upon wetting due to their mineralogical composition. The continuous swelling of soil can cause damages to the buildings and other structures constructed on it. It was reported that the damage and, thus the loss, due to expansive soils in many countries is more than the damage due to natural calamities. As the water from irrigation or rainfall seeps into the foundation soil, the swelling mechanism triggers, which is mainly responsible for pushing the structure gradually upwards as shown in Fig 1.12.