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Atterberg's Limits (consistency limits) and Liquid state, Plastic state, Semi-solid state, Soild state and Importance of Atterberg's Limits

Consistency limits is the relative ease with which soil can be deformed. This term is generally used for fine grained soils. 

 Consistency limits denotes "the degree of firmness of soil" Which may be termed as soft, firm, stiff. 
Consistency limits of fine grained soils is related to a large extent on water content. A soil which is very soft at a higher percentage of water contemt become very hard with the decrease of water content. 

 A Swedish agriculture engineer Atterberg's limits and consistency limits describe in 1911.That a fine grained soil can exist in four states namely;Liquid, Plastic, semi-solid and soild state. 

The water content at which the soil changes from one state to another state are known as Atterberg's limits and consistency limits. 

 Fine grained soil may be micmxed with to form a plastic paste which can be mould into any desired shape. The addition of water reduce the cohesion but the soil can still be moulded into different forms. 

 Further addition of water reduces and cohesion until the material no longer retained it's shape under it's own weight but flies as a liquid. Enough water may be added until the soil gaines are dispersed in a suspension. 

 If water is evaporated or removed from such a soil suspension the soil passes through different stages of consistency limits as mentioned below;

 1) Liquid state   e.g Thich juice
2) Plastic state  e.g Soft butter
3) Semi soils state  e.g cheese
4) Soild state e.g.chocolate 

 In liquid state, it flows like a thick juice. In plastic state, it can be given any shape like soft butter. 

 In semi-solid state, the soil cracks when moulded. Cheese is a typical example of this state. In this state, the volume of the soil decrease with a decrease in water content till a stage is reached when further reduction of the water content does not cause any type of reduction in the volume of the soil. This state of soil is Soils state. Hard chocolate is an example of solid state. 


 The important Atterberg's limits which are most useful for engineering purposes are;

 I) Liquid limit
2) Plastic limit
3) shrinkage limit

 Definitions of Atterberg's limits or consistency limits:

 The Atterberg's limits or consistency limits are expressed as percentage of water content. 

 1) Liquid limit: It is defined as the maximum water content at which the soil is still in the liquid state but has a small shearing resistance against flowing. 

 Or simply way "the water content at which soil changes from the liquid state to the plastic state is known as liquid limit. It is denoted by L. L. At this water content, soil ceases to be a liquid. 

 2) Plastic limit:It is defined as a Maximum water content at which the soil will just begin to crumble when rolled into a thread of approximately 3mm in diameter. 

 In simply way we can say that the water content at which the soil changes from plastic state to semi solid state is known as plastic limit. It is denoted by P. L. At this water content, soil just fails to behave as a plastic soil. 

 3) Shrinkage limit: It is defined as the maximum water at which a reduction in water content will not cause a decrease in the volume of a soil mass.

 simply the water content at which soil changes from semi soild state to the soild state is known as the shrinkage limit. At this water content, soil stops shrinkage further and attains a constant volume. 
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