Question

In the context of shear strength of soil, which of the following statements is/are CORRECT?

• A. The unconfined compression test is a special case of the unconfined-undrained (UU) triaxial tests.
• B. The shear strength parameters obtained from the consolidated-drained (CD) triaxial tests should be used to analyse rapid construction in clay.
• C. Vane shear test is commonly used for determining in situ undrained strength of saturated clay soils.
• D. In an unconsolidated-undrained (UU) triaxial tests, the angle of internal friction (\(\phi\)) is equal to zero.

Hint:

In soil mechanics, it is essential to select the correct type of test based on the nature of the soil and the conditions of the construction project. For undrained conditions, the UU test and vane shear test are often used.

Answer 1

The Correct Option is A, C, D

Analysis of Statements on Soil Testing

Statement (a):
The unconfined compression test is indeed a special case of the unconsolidated-undrained (UU) triaxial test.
- In the unconfined compression test, the confining pressure is zero, which makes it a particular case of the UU triaxial test.
- Hence, statement (a) is correct.

Statement (b):
The shear strength parameters obtained from the consolidated-drained (CD) triaxial tests should not be used for rapid construction in clay.
- The CD tests are performed on soils that consolidate over time and are more relevant to long-term stability.
- Rapid construction in clay requires parameters from unconsolidated-undrained (UU) tests.
- Hence, statement (b) is incorrect.

Statement (c):
The vane shear test is widely used for determining the in situ undrained strength of saturated clays.
- This test is particularly useful when samples cannot be easily retrieved for laboratory tests.
- Hence, statement (c) is correct.

Statement (d):
In an unconsolidated-undrained (UU) triaxial test, the internal friction angle (\(\phi\)) is assumed to be zero for saturated clays under undrained conditions.
- This assumption is based on the fact that pore water pressure buildup prevents effective stress changes.
- Hence, statement (d) is correct.

Final Answer:
Statements (a), (c), and (d) are correct, while statement (b) is incorrect.