What are the different types of triaxial tests and when are they used?

Triaxial tests apply confining pressure and axial load to cylindrical specimens. Types: (1) Unconsolidated Undrained (UU) - no drainage, fast, gives total stress parameters for immediate loading of clay, (2) Consolidated Undrained (CU) with pore pressure measurement - gives effective stress parameters for loading faster than drainage, (3) Consolidated Drained (CD) - full drainage, gives effective stress parameters for long-term stability. CU tests are most common, providing both total and effective strength parameters.