Define the Following

1) Consistency Index:-

It represents the effect of consistency on a shear strength/ Greater the consistency Index, Greater will be the shear strength of a soil

It is given by, $I_{e}=\frac{WL-W}{WL-WP}$=$\frac{WL-W}{I_{p}}$

Where, WL =liquid limit WP=Plastic limit W=water content

2)Flow Index:-

It is slope of flow curve obtained between water content and number of blows in casagrande's method of determination of liquid limit. It is given as follows

Flow Index(If)=$\frac{W_{1}-W_{2}}{log_{10}\frac{N_{2}}{N_{1}}}$

$N_{1}$=Number of blows at water content(w1) $N_{2}$=Number of blows at water content(w2)


The degree of disturbance achieved on remoulding is represented by sensitivity

It is defined as ratio of unconfined compressive strength of undisturbed soils to the unconfined compressive strength of remoulded soil

$s_{t}=\frac{unconfined \ compressive \ strength \ of \ undisturbed \ soil}{unconfined \ comp \ strength\ of \ Remoulded \ soil}$


$q_{u}$=unconfined compressive strength.

4) Toughness Index:-

It give idea about shear strength of soil at plastic limit. generally its value for most of the soil is in range of 0 to 3

It is defined as ratio of plasticity index to the flow Index.


5)Activity Number:-

It is defined as the ratio of plasticity Index to percentage of clay

A= $\frac{I_{p}}{fines \lt 0.002mm}$

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