What effect does moisture have on expansive soils?

Moisture has a significant effect on expansive soils, primarily because these types of soils — typically clay-rich — are highly responsive to changes in water content. When moisture is introduced to expansive soils, it causes the soil to swell. Conversely, when the moisture content decreases, the soil contracts. This phenomenon of volume change is critical for construction and engineering projects. It can lead to substantial ground movement, which may adversely affect structures built on or within these soils.

On the other hand, options referring to increases in structural integrity, decreases in erosion, or enhancements in drainage do not accurately represent the behavior of expansive soils in relation to moisture. Instead, these soils present challenges that must be addressed through careful design and engineering solutions to mitigate the adverse effects of moisture fluctuations. For instance, understanding that moisture causes volume changes helps in implementing measures like proper drainage and soil stabilization techniques to reduce the potential for damage to foundations and other structures.