What does the Plastic Limit (PL) indicate in soil mechanics?

The Plastic Limit (PL) in soil mechanics is defined as the moisture content at which the soil changes from a semi-solid state to a plastic state. This transition point signifies that the soil is still moldable but not overly saturated. Specifically, it is the moisture content at which the soil can be deformed without cracking.

When soil reaches its Plastic Limit, it can be rolled into threads without breaking, indicating that it has sufficient plasticity to be worked and shaped but is not too wet. This property is crucial for understanding the behavior of soils in terms of their plasticity and shear strength.

On the other hand, the choices regarding moisture content at which soil retains its shape pertain more to the Atterberg limits; the transition between solid and semi-solid reflects a different physical property, and the fully liquid state relates more to the Liquid Limit rather than the Plastic Limit. Therefore, the most accurate depiction of the Plastic Limit pertains to moldable soil, confirming that this is the correct interpretation.