The shear strength in plastic clay is due to:
Try it first: pick an option, then read the explanation.
Correct answer: C. cohesion
Asked in SSC JE 04/03/2017 (Evening)
Detailed Explanation
Clay particles are tiny, plate-shaped and carry electrical charges. In a plastic clay they are held together by attraction and by the bonds of the adsorbed water layers between them.
Why “cohesion” Is Correct
This attraction is called cohesion, and it is the main source of strength in plastic clays. Friction plays a much smaller role (especially under undrained loading, where φu ≈ 0).
Why the Other Options Are Wrong
- A. none of these: Plastic clay clearly has shear strength, mainly from cohesion.
- B. inter-granular friction: Inter-granular friction dominates in sands, not plastic clays.
- D. internal friction: Internal friction is a minor component in plastic clay.
Key Point
Sand → friction. Plastic clay → cohesion.
Key Concepts for Students
- Undrained strength of saturated clay = cu.
- Cohesion falls as water content rises.
- Remoulding reduces clay strength (sensitivity).
Practice more: this is question 39 in Shear Strength of Soils MCQs – Part 3. Try the whole set and check every answer instantly.