What type of soil usually requires specific engineering measures due to its expansive properties?

Clay is the correct answer because it has expansive properties that can significantly affect the integrity of structures built upon it. Clay soils can swell when saturated with water and shrink as they dry. This cyclic behavior can lead to ground movement, posing risks such as foundation settlement, cracking, or structural damage to buildings.

Due to these characteristics, specific engineering measures such as proper drainage, moisture control, or the use of deep foundations may be necessary to mitigate potential issues related to expansive clay soils. Engineers often conduct thorough soil analyses before construction to ensure that appropriate measures are implemented, preserving the stability and longevity of the structure.

In contrast, sand, silt, and gravel do not exhibit the same level of expansive behavior. Sand typically drains well and does not undergo the significant volume changes that clay does. Silt can retain moisture but doesn't expand like clay. Gravel offers good drainage and stability, making it less prone to the kinds of issues that arise with expansive clay soils.