What indicates high plasticity in soils?

High plasticity in soils is indicated by the ability to retain shape under pressure. This characteristic is a key property of plastic soils, which includes clays that can be molded when wet and retain their form once they dry or are compacted. The ability to maintain a stable shape without cracking or breaking shows that the soil has sufficient cohesion and plasticity, making it suitable for various engineering applications.

While high moisture content can contribute to the plasticity of a soil by making it more malleable, it is not a definitive indicator of plasticity on its own. Small particle size is associated with increased surface area and can enhance plasticity, but it is the behavior of the soil under pressure that ultimately defines its plasticity. Similarly, the absence of gravel can influence the overall composition of the soil; however, the presence of cohesive particles such as clay is what primarily determines plasticity. Therefore, the ability to retain shape under pressure is the most direct and relevant indicator of high plasticity in soils.