Which statement correctly describes the Liquid Limit (LL)?

• A. The behavior when clayey soil changes from plastic to liquid
• B. The behavior when clayey soil changes from liquid to solid
• C. The moisture content at which thread breaks apart at 1/8 inch
• D. The moisture content at which soil becomes gaseous

Answer: (A)

The liquid limit is the moisture content at which a clayey soil changes from plastic to liquid behavior. In the standard test, you adjust the soil’s water content and observe how it flows under a defined amount of deformation (the Casagrande test). The moisture content at which the soil just begins to flow and behave like a liquid under those conditions is the liquid limit. This concept captures a transition from a workable, bendable plastic state to a more fluid, cohesive liquid state, which is why it’s used to characterize the plasticity of clays and to compute indices like the plasticity index.

The other statements describe different concepts: the moisture content where a plastic-thread test indicates the plastic limit (not the liquid limit), the idea of the soil becoming gaseous is not a valid state in this context, and there isn’t a standard “liquid to solid” moisture state used in Atterberg limits.