What defines the cohesiveness of cohesive soil?

The cohesiveness of cohesive soil is primarily defined by its high clay content. Clay particles are very small and have a high surface area relative to their volume, which contributes to their ability to stick together due to electrostatic forces and water absorption. This results in cohesive soils being able to maintain their shape and structural integrity even when wet, giving them the characteristic of being cohesive.

In contrast, low moisture content can lead to a decrease in the soil's cohesive properties as it becomes harder and more rigid. Large particle size, typically found in sandy or granular soils, does not provide the fine particle interactions necessary for cohesiveness. Furthermore, the presence of gravel, which consists of larger aggregates, tends to disrupt the cohesive properties found in clay-rich soils, as gravel does not bind the way that fine clay particles do. Thus, the defining factor of cohesiveness in cohesive soils is their high clay content.