The commonly used strength test in the laboratory is the Tri axial shear test.

Tri axial shear test:
- The tri axial shear test is a laboratory test used to determine the shear strength of a soil sample. It is commonly used in geotechnical engineering to understand the behavior of soil under different loading conditions.
- In this test, a cylindrical soil sample is placed inside a tri axial cell which has a membrane that surrounds the sample. The cell allows for the application of a confining pressure on the sample.
- The test consists of applying a confining pressure to the sample and then shearing it along a predetermined plane. The shearing is usually done by applying axial and torsional loads to the cell.
- The test measures the shear stress and shear strain of the soil sample as it is sheared. From these measurements, the shear strength parameters such as cohesion and angle of internal friction can be determined.
- The tri axial shear test is considered more realistic than other strength tests because it takes into account the confining pressure that exists in the field. The confining pressure simulates the stress conditions that the soil experiences when it is in the ground.
- The results of the tri axial shear test can be used to design foundations, retaining walls, and other geotechnical structures that rely on the shear strength of the soil.
- The tri axial shear test is also used in research and development to study the behavior of soils under different loading conditions and to investigate the effects of various factors such as moisture content, stress history, and consolidation on the shear strength of the soil.

In conclusion, the tri axial shear test is commonly used in the laboratory to determine the shear strength of soil samples. It provides valuable information for geotechnical engineering design and research purposes.