Consistency of soil
In this article we discussed:-
Consistency it is the external work done required to convert the soil from one state to another.
Consistency limit
I. It is the water content at which soil changes form one state to another
II. It is also known as Atterberg’s limit
a) Liquid limit
b) Plastic limit
c) Shrinkage limit
Liquid Limit
I. It is the minimum water content at which the soil converts from plastic state to liquid state
II. At liquid limit, all the soils contains very small shear strength
Plastic limit
I. This minimum water content at which the soil is converted from semi solid to
plastic state.
Shrinkage Limit
i. it is the minimum water content at which a soil is convert from semi-solid state to
solid
ii. it is the water content below which volume of soil is constant
iii. At shrinkage limit & above water content, the soil is fully saturated.
iv. Below shrinkage limit ,the soil is partially saturated hence lies b/w 0 to 100.
1). Plasticity Index
Plasticity index represents the range of water content in which soil contains plastic properties.
IP = WL-WP
i. WL= WP -----> IP=0 Non-plastics soil e.g. sand
ii. WL> WP -----> IP = +Ve
iii. WL< WP -----> IP≠ -Ve -----> IP=0
Ip= plasticity index
WL = liquid limit
Wp = plastic limit
W = natural water content
IP Soil type Example
0 Non plastic soil sand
0-7 Low plastic soil Silt
7-17 Medium plastic Salty clay
>17 Highly plastic soil Clay
2). Consistency Index
Ic=WL-W/ IP
Ic= WL-WP /WL-WP
i. IC = 0 ------- >WL= W ------- > Soil is at liquid Limit
ii. IC = 1 ------- > WP = W ------- > Soil is at plastic limit
iii. 0<IC<1 ------- > soil is at plastic state
iv. IC>1 ------- > W<WP ------- > Semi-solid/solid
v. IC<0 ------- > W>WL ------- > Liquid state
3). Liquidity Index or Water plasticity Ratio
IL = W-Wp/Ip = W-Wp /WL-Wp
• IC+IL=1
Activity of Clay
• Activity of Clay is the ratio of plasticity index to percentage of particles less than 2µ.
This term is defined only for clay particle
• Activity of clay is the slope of curve b/w plasticity index & percentage particles less than 2µ.
• A= IP / (%C)
• Unit ------- > unit less
Activity
0-0.75 - inactive
0.75-1.25 - Normal
>1.25 Active (max shrinkage & swelling)(black cotton soil)
Sensitivity of clay –
It is the ratio of shear strength of soil for undisturbed condition to the shear strength of soil for disturbed condition
undisturbed /disturbed =Sr
Sensitivity of soul is always greater than 1
If Sr = 1 ------- >Insensitive soil
Thixotropy of clay
Thix ------ > To touch
• The process of strength loss & strength gain without any change in water content of soul is known as Thixotropy.
• The gain in strength is due to reformation of molecular crystals & structures.
