What is deviator stress in Triaxial test?

The deviator stress in a triaxial test is a measure of the difference in stress applied in the axial direction (vertical) and the radial direction (horizontal) on a cylindrical soil sample. It is used to simulate the different stresses that soil experiences in real-world conditions.

Here are the steps to understand it:

1. In a triaxial test, a cylindrical sample of soil is subjected to a confining pressure in the radial direction and an axial load in the vertical direction.

2. The confining pressure is applied first to simulate the overburden pressure that soil experiences in the ground. This pressure is applied equally in all radial directions.

3. The axial load is then applied. This simulates additional stresses that the soil might experience, such as from a building or other structure.

4. The deviator stress is calculated as the difference between the axial stress and the confining stress. It represents the additional stress that the soil is subjected to beyond the confining pressure.

5. The deviator stress is used in calculations to determine various soil properties, such as its shear strength and its ability to deform without failing.

6. The results of the triaxial test, including the deviator stress, can be used to design safe and effective foundations and other soil structures.