Soil Classification MCQ with answer and solution

Concept

As per IS 1498, particles smaller than 75 micron (0.075 mm) are fine grained (silt and clay).

Step-by-step solution

1. IS sieve 75 micron (0.075 mm) separates coarse and fine soil. 2. Particles passing the 75 micron sieve are silt and clay, called fines. 3. So fine grained soil has particle size less than 0.075 mm.

Explanation

IS 1498 uses the 75 micron sieve (0.075 mm) to separate coarse grained soil from fine grained soil. Silt and clay are smaller than 0.075 mm. So the answer is 0.075 mm.

Why the other options are wrong

A: 0.015 mm is not a standard IS boundary (silt-clay limit is 0.002 mm). B: 0.020 mm is not an IS boundary for fines. C: 4.75 mm separates gravel from sand, not sand from fines.

Shortcut

Remember: 4.75 mm separates gravel and sand, 0.075 mm separates sand and fines, 0.002 mm separates silt and clay.

Common mistake

Choosing 4.75 mm, which is the gravel-sand boundary, not the fine soil limit.