The moisture content at the phase wherein the state is transitioning from plastic to liquid state.

In soil mechanics, the moisture content at which soil transitions from a plastic state to a liquid state is referred to as the liquid limit (often denoted as $w_L$). This is a critical value in understanding the behavior of fine-grained soils, particularly clay.

1. Definition of Liquid Limit: The liquid limit is defined as the moisture content at which the soil changes from a plastic to a liquid state. At this point, the soil can flow and will no longer retain its shape when subjected to external forces.

2. Importance: Understanding the liquid limit is crucial for construction and civil engineering projects since soil behavior under varying moisture conditions can significantly impact the stability and integrity of structures.

3. Testing Procedure: The liquid limit is commonly determined using the Casagrande cup method or the dynamic cone penetrometer method, where the moisture content is varied, and the point at which soil can flow is identified.

4. Applications: Knowledge of the liquid limit helps in classification of soils and is part of the Atterberg limits, which are essential for predicting the engineering properties of soils.

Overall, the liquid limit indicates the moisture content threshold for a soil to transition from a workable, plastic nature to a less controllable liquid state, highlighting critical factors in soil management and engineering designs.