Atterberg limits and indices

In 1911 Atterberg defined the states of consistency in which a soil can exist. In passing from a “wet” to a “dry” condition, a soil goes from a liquid state through semiliquid, plastic, semisolid, and finally solid states. In the liquid state the soil has no shear strength. In the semiliquid state the soil resembles a viscous fluid and has practically no shear strength. In the plastic state the soil can be deformed without cracking and retains its deformed shape. As it passes into the semisolid state, the soil begins to crack and crumble with deformation. Finally, in the solid state the soil has all the characteristics of a solid. Atterberg referred to the transitional boundary between the semiliquid and plastic states as the upper plastic limit, and defined it as the level of Moisture Content where shear strength is just observed. The boundary between the plastic and semisolid states he called the lower plastic limit, defining it as the level of moisture content at which the soil just starts to crack and crumble with deformation. He defined the shrinkage limit as the level of moisture content at which the soil ceases to shrink with further drying, and called it the boundary between the semisolid and solid states (Atterberg, 1911). …