Shear Strength of Soils by Triaxial Test

A triaxial test is a novel technique for testing soil samples subjected to orthogonal stresses existing in the field under controlled drainage conditions. These orthogonal stresses are generally known as principal stresses (e.g. σ1, σ2, σ3, whereː σ2 = σ3). Since the DST has numerous limitations, therefore, A. Casagrande conceived the need for the triaxial test for reliable measurement of soil strength parameters. A triaxial test is a most suitable and widely used soil test in the geotechnical laboratory for evaluation of shear parameters (c & ɸ) under controlled drainage and loading conditions. These parameters are required in the design of various civil engineering structures under short-term and long-term stability analysis. The triaxial tests are mostly conducted on high-quality undisturbed soil samples and reconstituted soil samples under very high confined pressures or as desired based on a research problem. The triaxial tests are also conducted on rock samples. A triaxial test is highly preferred over the direct shear test and the soil sample fails along the weakest plane rather than on a pre-determined failure plane in case of a direct shear test.