Grain Size Distribution, Liquid, Plastic And Shrinkage Limit ~ Civil Engineer Knowledge

SOIL MECHANICS( Chapter 3)

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GRAIN SIZE DISTRIBUTION

Coefficient of uniformity = D60/D10

Coefficient of curvature =(D30)^2/( D10*D60)

Where, grain diameter at 60% passing,

grain diameter at 30% passing,

grain diameter at 10% passing.

When, 1<Cc<3 and Cu> 4 then, that is Gravel.
Cu> 6 for sand.
Cu= 1 for uniformity soil or poor graded soil.

1. Liquid Limit- The boundary of water content between the liquid state and plastic state is called Liquid Limit.

2. Plastic Limit- The boundary of Water content between plastic state to semisolid state is called Plastic Limit.

3. Shrinkage Limit- The boundary of Water content between plastic state to semisolid state is called Shrinkage Limit.

Liquid Limit = WL, Plastic Limit = Wp
V1 = Volume of soil mass at Liquid limit.
Vp = Volume of soil mass at plastic limit.
Vd = Volume of soil mass at Shrinkage Limit.
Vs = Volume of the solid.

1. Plasticity Index(Ip)-

Ip = WL- Wp , For course grain soils, Ip = 0.

2. Consistency Index or Relative Consistency (Ic)-
Ic = (WL - WN)/ Ip Where, WN = Natural water content.
For WN = WL , then Ic = 0.
And WN= Wp , then Ic = 1.
Whem Ic< 0 , Natural water content of soil(WN) > WL.
Ic > 1, Soil very hard or stiff.

3. Liquidity Index(IL)-
IL = (WN- WP)/Ip

4. Flow Index(f)-
f = ( W1-W2)/ log(N2/N1)

5. Toughness Index(IT)-
IT = Ip/If 0 <IT< 3

6. Shrinkage Ratio(SR)-
SR = ((V1- V2)/Vd*100)/(W1-W2)
V1 = Volume of soil mass at moisture content W1%.
V2 = Volume of soil mass at moisture content W2%.
Vd = Volume of dry soil mass.

7. Relative Index or Density Index(Dr)-

Dr = (Emax - E)/(Emax - Emin)

Emax = void ratio at loosest state.

Emin = void ratio at densest state.

8. Activity-

Activity of clay = Plasticity Index/ % of clay.

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