What is the reason for preferring the triaxial shear test over the direct shear test?

What is the reason for preferring the triaxial shear test over the direct shear test? Correct Answer Test can be performed under all three drainage conditions with complete control.

Concept:

A triaxial shear test is preferred over direct shear test because of following reasons –

1. Triaxial test has complete control over drainage conditions. Test can easily be conducted for all three types of drainage conditions.

2. Precise measurement of pore pressure and change in volume during the test is possible.

3. Stress distribution is uniform on the failure plane.

4. The specimen will fail along weakest plane while in direct shear test failure can occur along the plane which is not the weakest.

5. Mohr circle can be drawn as the stresses at all the intermediate state is known up to failure.

Note: -

Demerits of triaxial test –

The following are the demerits of triaxial test -

1. Takes longer period under drainage condition than direct shear test.

2. Uneconomical

3. No accurate measurement of cross-section area of specimen under large strains.