The determination of shear strength of a soft saturated clay deposit in the field can be done by:
Try it first: pick an option, then read the explanation.
Correct answer: B. the vane shear test
Asked in SSC JE 23/03/2021 (Morning)
Detailed Explanation
Soft, sensitive clays are easily disturbed by sampling, so laboratory tests on ‘undisturbed’ samples often underestimate their strength. An in-situ test avoids that problem.
Why “the vane shear test” Is Correct
The vane shear test is performed directly in the ground, at the bottom of a borehole or by pushing the vane in. It measures the undrained strength of soft clay without removing a sample, which is why it is the field test of choice.
Why the Other Options Are Wrong
- A. the triaxial test: Triaxial tests are laboratory tests on samples brought from the field.
- C. the unconfined compression test: Unconfined compression is also a laboratory test, and soft clay samples may not even stand unsupported.
- D. the direct shear test: Direct shear is a laboratory test and is mainly used for sands.
Key Point
Soft clay, field, undrained strength → vane shear test.
Key Concepts for Students
- Suitable for clays with cu up to about 100 kPa.
- Not suitable for sands, gravels or clays with stones and fissures.
- Gives both peak and remoulded strength (and hence sensitivity).
Practice more: this is question 20 in Shear Strength of Soils MCQs – Part 2. Try the whole set and check every answer instantly.