Question

The water content at which soil changes from liquid state to plastic state is known as

• A. Plastic limit
• B. Liquid limit
• C. Shrinkage limit
• D. Plasticity Index

Hint:

Casagrande apparatus: Standard 25 blows to close the groove by 12.7 mm determines the Liquid Limit ($LL$).

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Atterberg limits define critical boundary moisture contents dividing the mechanical behavior states of fine-grained cohesive soils.
Key Formula or Approach:
\[ \text{Solid} \xrightarrow{SL} \text{Semi-solid} \xrightarrow{PL} \text{Plastic} \xrightarrow{LL} \text{Liquid} \]
\[ I_p = LL - PL \]

Step 2: Detailed Explanation:
The four distinct consistency states and their boundary moisture contents are:
1. Liquid Limit (LL): The moisture content boundary at which soil transitions from the liquid state to the plastic state (measured using Casagrande's apparatus or cone penetrometer).
2. Plastic Limit (PL): The moisture content boundary between the plastic state and semi-solid state (where a 3 mm thread begins to crumble).
3. Shrinkage Limit (SL): The moisture content below which further moisture loss causes no further volume reduction.

Step 3: Final Answer:
Thus, the transition boundary between liquid and plastic states is the Liquid limit, corresponding to option (B).