The triaxial test is usually carried out as:
Try it first: pick an option, then read the explanation.
Correct answer: D. All of the above
Asked in SSC JE 2007
Detailed Explanation
One of the main advantages of the triaxial apparatus is complete control over drainage, so it can be used in several ways depending on the field problem.
Why “All of the above” Is Correct
Unconsolidated undrained (quick), consolidated undrained and consolidated drained tests are all run in the triaxial cell. Since the options listed are all forms in which the test is carried out, ‘all of the above’ is correct.
| Test | Drainage during consolidation stage | Drainage during shear | Typical use |
|---|---|---|---|
| UU (unconsolidated undrained, ‘quick’) | Not allowed | Not allowed | End-of-construction / immediate stability of saturated clays |
| CU (consolidated undrained) | Allowed | Not allowed (pore pressure can be measured) | Rapid drawdown, staged loading |
| CD (consolidated drained, ‘slow’) | Allowed | Allowed | Long-term stability; effective-stress parameters c′, φ′ |
Unconfined compression is a special UU test with zero cell pressure (σ₃ = 0).
Why the Other Options Are Wrong
- A. Unconsolidated undrained test: UU is only one of the forms.
- B. Consolidated undrained test: CU is only one of the forms.
- C. Undrained test: Undrained tests are only some of the forms.
Key Point
Triaxial: UU, CU, CD.
Key Concepts for Students
- Choose the test to match field drainage.
- CU with pore pressure measurement is the most informative.
- CD tests on clays can take days.
Practice more: this is question 48 in Shear Strength of Soils MCQs – Part 4. Try the whole set and check every answer instantly.