What is defined as the water content at which soil transitions from a plastic to a liquid state?

The water content at which soil transitions from a plastic to a liquid state is known as the liquid limit. This measurement is critical in soil mechanics, as it indicates the moisture content at which the soil ceases to behave as a plastic material and begins to behave like a fluid. The liquid limit is determined through a standardized test that typically involves the use of a cone penetrometer or a flow table, where the soil's properties are assessed under varying water contents.

Understanding the liquid limit is vital for engineers and technicians as it helps characterize the material's behavior under different moisture conditions, which is essential for foundation design, earthwork, and construction activities. This limit is part of what is collectively known as the Atterberg limits, which also includes the plastic limit and the shrinkage limit, but specifically, the liquid limit focuses solely on the transition from plasticity to fluidity.

The distinction made by the liquid limit helps in classifying soils and predicting their behavior in construction and engineering applications.