What type of soil is generally considered less stable for excavations?

Clayey soils are generally considered less stable for excavations due to their unique properties. When wet, clayey soils can become highly plastic and lose strength, making them prone to deformation. These soils tend to have a high water retention capacity, which can lead to changes in their consistency and stability. When excavated, clayey soils can easily slump or collapse because they do not provide the same level of immediate support as other soil types. Additionally, clay's cohesive nature can lead to challenges in maintaining the walls of an excavation, especially during wet conditions, increasing the potential for unsafe working environments.

Granular soils, rocky soils, and sandy soils typically have better drainage and are less likely to change significantly in stability due to moisture content. They tend to have more open structures that provide better support during excavations, making them generally more stable options in comparison to clayey soils.