What is a key characteristic of expansive soil?

A key characteristic of expansive soil is its ability to undergo significant volume changes in response to moisture content variations. This means that when expansive soil absorbs water, it swells, and when it dries, it contracts. This cyclical behavior can lead to structural issues if the soil is used improperly in construction.

Using expansive soil as backfill can lead to problems, such as excessive heaving or settling, which can compromise the stability of foundations, pavements, and other structures built on or near it. Therefore, it is generally advised to avoid using expansive soil for backfill to mitigate these risks. Proper soil selection is crucial for ensuring the longevity and safety of construction projects.

The other options do not accurately reflect the nature of expansive soil, particularly regarding its inappropriate use as backfill, showcasing why understanding its properties is essential in construction practices.