1.

What is Group index of soil and how do you find it?

Answer»

Group Index is a number assigned to the soil BASED on its PHYSICAL properties like particle size, Liquid LIMIT and plastic limit. It VARIES from a value of 0 to 20, lower the value higher is the quality of the sub-grade and greater the value, poor is the sub-grade.

By sieve analysis test we can determine Group index value of soil SUBGRADE from below equation

GI = 0.2a + 0.005 ac + 0.01bd

Where,

a= percentage of soil passing 0.074 mm sieve in excess of 35 per cent, not exceeding 75.

b= percentage of soil passing 0.074 mm sieve in excess of 15 per cent, not exceeding 55.

c= Liquid limit in per cent in excess of 40.

d= Plasticity index in excess of 10.


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