Question

In a soil specimen, 70% of particles are passing through 4.75 mm IS sieve and 40% of particles are passing through 75μ IS sieve. Its uniformity coefficient is 8 and coefficient of curvature is 2. As per IS classification, this soil is classified as:
1. GW
2. SP
3. GP
4. SW

Answer 1

Correct Answer - Option 4 : SW

Explanation

1. If fraction of soil passing through 0.075 mm sieve is more than 50 % than soil is classified as fine grained otherwise coarse grained.

It is given that only 40 % particle passes through 0.075 mm sieve so it is coarse grained soil.

2. Coarse grained soil can further be classified in to gravel and sand. If more than 50% of soil passes through 4.75 mm then it is sand.

In this case, 70 % of particles are passing through 4.75 mm, so it is sand.

Note:

When 70% passed 4.75 mm sieve then 30% gravel correct But now for sand and fine grained (0.075 mm) classification we should take 40% of 70 % (as only 70% is passed from 4.75 mm) i.e 28% passed 0.075 mm (silt + clay) and (70 - 28)% = 42% retained 0.075 mm that is sand.

3. Sand is said to be well graded is uniformity coefficient (C_u) is greater than 6 and coefficient of curvature (C_c) lies in between 1 to 3.

Gravel is said to be well graded is uniformity coefficient (C_u) is greater than 4 and coefficient of curvature (C_c) lies in between 1 to 3.

In this case our soil is sand and it is given as C_u = 8 i.e. > 6 and C_c = 2 (lies in between 1 and 3) so it is well graded sand or SW.