The unconfined strengths of three types of cohesive soils, Soil A, Soil B and Soil C, are 35 kN/m², 450 kN/m² and 140 kN/m² respectively. Identify the correct statement based on the consistency behaviour of soils.
Try it first: pick an option, then read the explanation.
Correct answer: C. Soil A is soft, soil B is hard and soil C is stiff
Asked in SSC JE 11/12/2020 (Evening)
Detailed Explanation
The consistency of a clay (how soft or hard it feels) is classified from its unconfined compressive strength qu, using standard ranges.
Why “Soil A is soft, soil B is hard and soil C is stiff” Is Correct
Soil A (35 kN/m²) lies in 25–50, so it is soft. Soil B (450 kN/m²) is above 400, so it is hard. Soil C (140 kN/m²) lies in 100–200, so it is stiff. That matches option (c).
| Consistency of clay | Unconfined compressive strength qu (kN/m²) |
|---|---|
| Very soft | < 25 |
| Soft | 25 – 50 |
| Medium (firm) | 50 – 100 |
| Stiff | 100 – 200 |
| Very stiff | 200 – 400 |
| Hard | > 400 |
Why the Other Options Are Wrong
- A. Soil A is soft, soil B is stiff and soil C is hard: Soil B (450) is hard, not stiff, and soil C (140) is stiff, not hard.
- B. Soil A is hard, soil B is stiff and soil C is soft: Soil A (35) is soft, not hard.
- D. Soil A is stiff, soil B is hard and soil C is soft: Soil A (35) is soft, not stiff, and soil C (140) is stiff, not soft.
Key Point
Remember the doubling ladder: 25, 50, 100, 200, 400 kN/m².
Key Concepts for Students
- Undrained shear strength cu = qu/2.
- A soft clay can be moulded by light finger pressure; a stiff clay needs strong pressure.
- Consistency ranges help pick foundation types quickly in preliminary design.
Practice more: this is question 25 in Shear Strength of Soils MCQs – Part 2. Try the whole set and check every answer instantly.