What are Atterberg limits and what do they indicate?

Atterberg limits define moisture content boundaries for soil consistency states. Liquid Limit (LL) is the water content at which soil transitions from plastic to liquid state. Plastic Limit (PL) is where soil changes from semi-solid to plastic state. Shrinkage Limit (SL) is where further drying causes no volume change. Plasticity Index (PI = LL - PL) indicates range of water content over which soil remains plastic. Higher PI indicates more clayey, potentially problematic soil.