Question

What is Group index? What is the data required for finding Group index of a soil?

Answer 1

It represents the performance of soil used in the construction of highways & roadways.

Greater the value of Group Index poor will be the quality of soil .

It consider the following parameters in determining the value of GI.

1.particles size

2.liquid limit

3.plasticity Index

GI=0.2a+0.005ac+0.01bd

a= Particle passing 75µ greater than 35% but not exceeding 75%( value lies between 0-40)

b=particle passing 75µ greater than 15% but not exceeding 55%(0-40)

c=value of liquid limit greater than 40% but not exceeding 60%(0-20)

d= value of plasticity index greater than 10% but not exceeding 30%(0-20)

. The minimum value of group index is zero & maximum value is 20

. GI value Quality

. 0-2. good

. 2-5. fair

. 5-10. poor

. 10-20. very poor