Shrinkage Ratio
It is a ratio of change in the volume expressed as the percentage of the dry volume to the corresponding change in the water content.
If Vd = volume of dry soil,
It is a ratio of change in the volume expressed as the percentage of the dry volume to the corresponding change in the water content.
If Vd = volume of dry soil,
Activity
It is the ratio of plasticity index and percentage of clay fraction.
A = Ip / F
where, F = percentage of clay fraction
If A < 0.75, the soil is inactive.
0.75 < A < 1.25, the soil is normal.
A > 1.25, the soil is active.
It is the ratio of plasticity index and percentage of clay fraction.
A = Ip / F
where, F = percentage of clay fraction
- A increases with F.
If A < 0.75, the soil is inactive.
0.75 < A < 1.25, the soil is normal.
A > 1.25, the soil is active.
Thixotropy
If the disturbed soil sample is allowed to stand without further disturbances and change in water content, it will regain some of its shear strength, which is known as thixotropy.
It (Toughness index) = Ip (Plasticity index) / If (Flow index)
If the disturbed soil sample is allowed to stand without further disturbances and change in water content, it will regain some of its shear strength, which is known as thixotropy.
It (Toughness index) = Ip (Plasticity index) / If (Flow index)
- Value ranges from 0 to 3.
- It is a measure of shear strength of the soil.
Uses of Consistency Limits
- The compressibility of soil increases with liquid limit.
- The liquid limit and plastic limit increase with decrease in particle size.
- The plasticity index is a measure of clay content of soil.
- The shrinkage limit is helpful in estimating the change in volume of soil below foundation after construction.
- The shear strength decreases with an increase in the plasticity index.
- The organic content increases the plastic limit.
- If the liquid limit is less than 20, the soil is termed as sand.
- If the plasticity indexes of two soils are same, the dry strength decreases with increase in liquid limit.