0
Plasticity of soil
• Plasticity of soil is its ability to undergo deformation without Cracking on Fracturing.

Engineering Properties :-

• The main engineering properties of soil are

• Permeability :- Indicates facility with which water can flow through soils.

• Compressibility :- Related to the deformation preocedure in soil (C.L)

• Shear Strength :- Shear strength of soils is its ability to resist shars strees.

Determines:-

1.Stability of slope

2.Bearing capacity of soil.

3.Earth presure on returning soils.

Index Properties

1. The test required for determination of engineering properties are generally elaborate and time consuming.

2. Sometimes Geotechnical engineer is interested into the rough assesment of engg properties without considering / conducting elaborate tests.

3. The properties of soils which are not of primary interest to the geotechnical engineer but which are indicative of the engg properties are called as index properties.

Main index proper

1. Eco grained soil - Relative Density particle size
2. Fine-grained soil - Atterberg limits & consistency

Atterberg Limits :- The Atterberg limits are a basic measure of the critical water content of the fine grained soils. Its shrinkage limit, plastic limit,and liquid limit.

Plasticity of soils:-

• Plastic soil can be moulded into various shapes when its wet.
• Plasticity isan important index properties of fine grained soils especially clay.
• Plasticity is due to presence of clay.

Consistency Limits:-

• Consistency of soils means degree of backbone firmness of soil.
• In 1991, a swedish agriculture engineer Atterberg mentioned that fine grained soil can be exist in four states.
Namely - Liquid ,Plastic, Semi-solid,and Solid state.
• The water content or moisture content at which the soils charges from one state to another are known as consistency limit or Atterberg limit.
1. Liquid limit:
-The water content at which the soils changes from liquid state to plastic state.
OR
-Limit is water content at which soil.
• Liquid Limits-->Determine
(A)Casagrande's apparatus (B)Cone peniration test
-The liquid limit of soils depend upon class mineral presents.

A. It is easier to perform.

B.The method is applicable for wide range of soils.

C. The results are reliable and de not depend upon the judgement of the operator.

• Plastic Limits:-

Plastic limit is the water content below which the soil stop behaving as a plastic limit.

$S=\frac{VW}{VV} -\gt\frac{watr}{voids}$

Completely saturation is occur when s>1
So partial saturated means when value of S is between 0-1
Partial Structure---> (0<=S<1)

• The water content at which the soil changes from one state to another is known as consistency limit or Atterberg Limit.
• A soils containing high water content is in liquid state.
• It offer no shearing resistance and can flow line liquid.
• It has no resistance to shear deformation and therefore the shear strength equal to zero.
• The water contents at which the soil changes from liquid state to plastic state is known as liquid state. OR
• In other words the liquid limit is the W.C at which soil access to be liquid.

(A) Plastic State

• The soil is in plastic state can be moulded into various shapes.
• As the water content is reduced, the plasticity of the soil decreases.
• Ultimately,the soil posses from the plastic state to semi-solid state when its stop behaving as plastics.
• The water content at which soil become a semi-solid is known as plastic limit. OR
• Plastic limit is water content at which the soil test fails to behave plastically.

The numerical difference between liquid limit state.& plstic limit is known as plasticity index. The soil remain plastic .when the water content is between liquid limit to plastic limit. PI=LL-PL (A) Semi solid state :-

• When the soil sample reduce below the plastic limit, soil attain a semi-solid state.The soil chokes when moulded.
• In this (semi-solid state) the volume of soil decrease with declare in water content till the stage is reached when further reduction of water content does not caused any reduction in the volume of soil.

• The water content at which the soil change from semi-solid state to solid state is called as shrinkage limit.
• Below the shrinkage limit soil does not remain saturated.
• Shrinkage limit may be also defined as lowest water content at which the soil is fully saturated.

Shrinkage limit :- $W_s$ =$\frac{(m1-m2)-(v1-v2)\rho n}{ms}$

Where m1,m2= mass

page plasticity of soil • 72  views