The correct answer is A.
A triaxial shear test is preferred to direct shear test because it can be performed under all three drainage conditions with complete control. This means that the test can be conducted under undrained, drained, or partially drained conditions, which allows for a more accurate assessment of the soil’s shear strength. Additionally, the triaxial shear test provides more information about the soil’s behavior, such as its stress-strain relationship and its pore pressure response.
The direct shear test is a simpler test that is often used to determine the shear strength of soils. However, it is limited in that it can only be conducted under undrained conditions. This means that the test does not provide information about the soil’s stress-strain relationship or its pore pressure response. Additionally, the direct shear test is more susceptible to errors than the triaxial shear test.
Here is a brief explanation of each option:
- Option A: This is the correct answer. The triaxial shear test can be performed under all three drainage conditions with complete control, which allows for a more accurate assessment of the soil’s shear strength.
- Option B: This is incorrect. Precise measurement of pore pressure and change in volume during test is possible in a triaxial shear test.
- Option C: This is incorrect. Stress distribution on the failure plane is uniform in a triaxial shear test.
- Option D: This is incorrect. None of the other options are correct.