In a triaxial compression test on a soil specimen, the intermediate principal stress is equal to:
Try it first: pick an option, then read the explanation.
Correct answer: B. minor principal stress
Asked in SSC JE (previous year paper)
Detailed Explanation
In triaxial compression the specimen is loaded vertically by σ₁ = σ₃ + σd, while cell pressure acts on all its sides.
Why “minor principal stress” Is Correct
The two horizontal principal stresses are both equal to the cell pressure. One of them is called the intermediate principal stress σ₂ and the other the minor σ₃, so σ₂ = σ₃ — the intermediate principal stress equals the minor principal stress.
Why the Other Options Are Wrong
- A. major principal stress: σ₁ is larger than the horizontal stresses during compression.
- C. difference between major and minor principal stresses: σ₁ − σ₃ is the deviator stress.
- D. none of these: Option (b) is correct.
Key Point
Triaxial compression: σ₂ = σ₃ = cell pressure.
Key Concepts for Students
- Axisymmetric condition.
- In triaxial extension, σ₁ = σ₂ = cell pressure instead.
- Same idea as Q306.
Practice more: this is question 53 in Shear Strength of Soils MCQs – Part 4. Try the whole set and check every answer instantly.