Question

The water content at which soil just begins to crumble when rolled into threads of 3 mm in diameter is known

• A. Liquid Limit
• B. Plastic Limit
• C. Shrinkage Limit
• D. Permeability Limit

Hint:

Atterberg limits are vital for classifying fine-grained soils and understanding their engineering properties such as compressibility, shear strength, and compaction characteristics. These limits are empirical but widely used in geotechnical engineering practice.

Answer 1

The Correct Option is B

Step 1: Understand the Atterberg Limits.
Atterberg limits are a series of tests performed on fine-grained soils to determine their consistency and behavior with varying water content. These limits define the boundaries between different states of soil consistency:

• Liquid Limit (LL): The water content at which a soil passes from a plastic state to a liquid state and possesses a very small shear strength. It is conventionally determined using the Casagrande liquid limit device or cone penetrometer.
• Plastic Limit (PL): The minimum water content at which a soil can be rolled into a thread of 3 mm (or 1/8 inch) diameter without crumbling. It marks the boundary between the plastic and semi-solid states.
• Shrinkage Limit (SL): The maximum water content at which a reduction in water content will not cause a decrease in the volume of the soil mass. It is the boundary between the semi-solid and solid states.

Step 2: Relate the given description to the definitions of Atterberg Limits.
The question states: "The water content at which soil just begins to crumble when rolled into threads of 3 mm in diameter". This specific criterion is the standard definition of the Plastic Limit (PL).
Step 3: Evaluate the other options.

• Liquid Limit: Incorrect, as it describes the transition from plastic to liquid state.
• Shrinkage Limit: Incorrect, as it describes the water content below which volume no longer changes.
• Permeability Limit: This is not one of the Atterberg limits. Permeability is a measure of how easily water flows through the soil.

Step 4: Select the correct option.
Based on the definition, the correct answer is Plastic Limit. $$\boxed{\text{Plastic Limit}}$$