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Activity of Soil

Activity of Soil :- ($A_t$)

(Scientist:-Skemptom)

Activity of soil os the ratio of plasticity index and percentage of clay friction (minus 2 cu size)

$A_t=\frac{I_p}{f}$

where,

$I_p=$Plastic index

$f=$clay friction

$A_t=\frac{W_l-W_p}{C%}$

where, $C%=$% of soil passing 2 cu size =% of soil finear than 2 mu $\lt 2u \rightarrow clay$

Conclusion:

$A_t \propto (W_l-W_p)-plasticity$

$\propto Wl$ (Its compressibility)

So,

If activity of soil is more then this soil will be more compressible or highly compressible.

Represented $\rightarrow$ shrinkage & swelling property of soil

• The clay friction F is % finer than 2 u size
• The amount of water is a soil mass depend upon the type of clay mineral present.
• Activity is a measure of the water holding capacity of clay soil. The changes in the volume of a clay in soil during swelling or shrinkage depends upon activity.

The soil containing the clay mineral:

• Kaolinite
• Ilite
• Montomorillonite

• The soil containing the clay mineral montomorillionite have been main activity $(A\gt4)$

• The soil contains the mineral Kaolinite are least active $(A\lt 1)$

• Whareas soil containing the mineral Illite are moderately active $(A=1 to 2)$

• Depending on the activity, the soils are classified into three types.

Sr. No. Activity Soil Type
1 A$\lt$0.75 Inactive
2 A=0.75 to 1.25 Normal
3 A$\gt$1.25 Active
• Activity gives information about the type of effect of class mineral in a soil. The following two points are worth nothing.
• For a soil of specific origin. the activity is constant. The plastic index (P.I.) increases as the amount of class friction increases.
• Montomorillonite can produce a large increase in the plasticity even when present in small quantity.
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