Question

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

Answer 1

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.

Answer 2

Group Index of soil

• Explanation:
• The group index of soil is defined as the value or number that is given to different varieties of soil on the basis of its physical properties like plastic limit, size of the particles, etc.
• It determines the characteristics of the soil including its gradation and plasticity.
• It is calculated by the formulae:
• GI(Group Index) = 0.2a + 0.005 ac + 0.01bd

where "GI = group index, a = 'percentage of soil passing 0.074 mm sieve in excess of 35%, not more than 75' b= % of soil passing 0.074 mm sieve in excess of 15%, not exceeding 55; c = Liquid limit in % in excess of 40; d= Plasticity index in excess of 10."

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