In a Triaxial Compression test, if the pore water pressure is measured, the test is called
- AUnconsolidated Undrained (UU)
- BConsolidated Undrained (CU)Correct
- CConsolidated Drained (CD)
- DUnconfined Compression Test
Solution
Concept
Consolidated undrained triaxial test with pore pressure measurement
Formula
σ' = σ - u
Step-by-step solution
1. In triaxial testing, a Consolidated Undrained (CU) test consolidates the specimen under confining cell pressure. 2. During the subsequent shearing phase, drainage valves are closed (undrained condition). 3. An electronic pressure transducer measures excess pore water pressure generated during shear. 4. This test allows determination of effective stress shear parameters (c' and φ'). Answer: B
Explanation
In a Consolidated Undrained (CU) triaxial compression test, the soil specimen is first allowed to consolidate under the cell pressure (drainage open). During the subsequent shearing stage, drainage valves are closed and pore water pressure generated inside the specimen is continuously measured to evaluate effective shear parameters.
Why the other options are wrong
A) Standard UU test measures total stresses quickly without pore water pressure dissipation or measurement. C) In CD tests, drainage is open and pore water drains freely with zero excess pore pressure. D) Unconfined compression test has no confining pressure (σ3 = 0).
Shortcut
CU test with pore pressure measurement = Effective stress Mohr-Coulomb parameters.
Common mistake
Confusing CU test with CD test where drainage is open and pore pressure is allowed to dissipate completely.
Correct answer: B) Consolidated Undrained (CU)