What is a common characteristic of clay soils?

Clay soils are known for their unique physical properties, particularly their ability to change volume significantly with varying moisture content. When clay is wet, it absorbs water and expands, which can lead to swelling. Conversely, when it dries out, it can shrink, leading to a reduction in volume. This characteristic makes clay soils particularly challenging in construction and engineering, as the changes in volume can affect the stability and integrity of structures built on or with them.

In contrast, the other options do not accurately describe clay soils. While clay does absorb water, it is not correct to say that it does not absorb water, as that is a characteristic of other soil types. Clay soils can also experience stability issues, especially when they are saturated with water or when they undergo significant volume changes. Additionally, clay is not primarily sandy in texture; rather, it consists of very fine particles that give it its cohesive nature. Thus, the characteristic of changing volume with moisture content is what fundamentally defines clay soils.