For determining the shear strength parameters of soil in the laboratory which of the following test has to be done?
- ATriaxial compression testCorrect
- BSieve analysis
- CCompaction test
- DRelative Density test
Solution
Concept
The shear strength parameters c and φ are found from shear tests such as the triaxial, direct shear and unconfined compression tests.
Formula
τf = c + σ tanφ
Step-by-step solution
1. The shear strength parameters are cohesion c and angle of shearing resistance φ. 2. The triaxial compression test loads samples at different confining pressures until failure. 3. Mohr circles are drawn and their common tangent gives c and φ. 4. The other options measure gradation, density or OMC, not shear strength.
Explanation
The triaxial test is the standard laboratory test for finding c and φ of soil. It tests samples at different cell pressures until failure, and the Mohr circles give the strength envelope. The other tests give index or compaction properties only.
Why the other options are wrong
B: Sieve analysis gives the grain size distribution. C: The compaction test gives OMC and maximum dry density. D: The relative density test gives the denseness of granular soil.
Shortcut
Shear parameters c and φ: think triaxial, direct shear, vane shear or UCS.
Common mistake
Confusing the compaction test with a strength test.
Correct answer: A) Triaxial compression test