What are expansive soils primarily characterized by?

Expansive soils are primarily characterized by their ability to swell significantly when they become wet, particularly when exposed to large amounts of water. This unique property is due to the clay minerals present in these soils, which can absorb water and expand in volume. When dehydrated, these soils contract, creating a cycle of swelling and shrinking that can have serious implications for structures built on such soils, as the movement can lead to cracks and structural damage.

This characteristic behavior of expansive soils differentiates them from other soil types that may not exhibit such dramatic changes in volume with moisture variations. Soils that are resistant to water, remain stable regardless of moisture, or are predominantly sandy do not encapsulate the fundamental nature of expansive soils, which is defined specifically by their response to water saturation.