What characterizes Expansive Soils?

Expansive soils are specifically characterized by the presence of significant amounts of expansible-layer clay minerals, such as montmorillonite. These clay minerals have the unique ability to absorb water and expand in volume when wet, and conversely, they shrink when dry. This cycle of expansion and contraction can lead to considerable ground movement, which can affect the stability of structures built on such soils. Recognizing the presence of these expansive-layer clay minerals is crucial for engineering and construction, as they can pose challenges in foundation design and site preparation.

In contrast, factors such as moisture content, drainage capabilities, and the absence of clay minerals do not define expansive soils. While low moisture content might be associated with non-expansive soils, expansive soils can exhibit significant moisture variability. Likewise, while well-draining soils are typically not expansive, there are expansive soils that may still retain enough moisture to expand. Clay minerals are fundamental to understanding expansive soils, as their presence is the key feature distinguishing them from other soil types.