Atterberg Limits
Liquid Limit Test | Plastic Limit Test

• Liquid limit: The boundary between the liquid and plastic states;

• Plastic limit: The boundary between the plastic and semi-solid states;

• Shrinkage limit: The boundary between the semi-solid and solid states.

Procedure for Determination of Liquid Limit | Procedure for Determination of Plastic Limit

These limits have since been more definitely defined by A. Casagrande as the water contents which exist under the following conditions:

• 1. Liquid limit

The water content at which the soil has such a small shear strength that it flows to close a groove of standard width when jarred in a specified manner. The Liquid Limit, also known as the upper plastic limit, is the water content at which soil changes from the liquid state to a plastic state. OR It is the minimum moisture content at which a soil flows upon application of very small shear force. Liquid Limit (LL or wL) ‑ the water content, in percent, of a soil at the arbitrarily defined boundary between the semi‑liquid and plastic states.

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Liquid limit is defined as “ the moisture content at which soil changes from liquid state to plastic state”

Or

According to Casagrande Liquid Limit Test it is also defined as “ the moisture content at which two sides of a groove come close together for a distance of 12.7 mm under the impact of 25 number of blows”

Or

According to fall cone test method Liquid Limit is also defined as “the moisture content at which the cone( fall cone test) penetrates with in the soil for 1 cm when falls freely for 5 seconds.

• 2. Plastic limit

The water content at which the soil begins to crumble when rolled into threads of specified size. The Plastic Limit, also known as the lower plastic limit, is the water content at which a soil changes from the plastic state to a semisolid state. Plastic Limit (PL or wP) ‑ the water content, in percent, of a soil at the boundary between the plastic and semi‑solid states.

It is defined as “The moisture content at which the soil behaves like a plastic material is called plastic limit”

Or

It may also be defined as “The moisture content at which the soil changes from plastic state to semi solid state"

Or

“The moisture content at which the soil begins to crumble when rolled up into a thread of 3 mm in diameter”

• 3. Shrinkage limit: Shrinkage limit is defined as “the moisture content at which the soil change from a semi solid state to a solid state”

Or

“The maximum water content at which the reduction in water content will not cause decrease in total volume of soil but the increase in moisture content will cause an increase in moisture content”

Or

It is also defined as “the lowest water content at which the soil are still completely saturated”

• 4. Plasticity Index (PI) ‑ the range of water content over which a soil behaves plastically. It is defined as “the range of consistency with in which the soil exhibit plastic properties”.

Or

It is also defined as “the numerical difference between the liquid limit and plastic limit”.

Mathematically, Plasticity index = Liquid Limit – Plastic Limit

It is denoted by I_p and

I_p = LL – PL

• 5. Liquidity index: Its advantage is that The liquidity index (LI) is used for scaling the natural water content of a soil sample to the limits.
• 6. Flow index
• 7. Toughness index