State-of-the-Art Paper: Some Recent Developments in Triaxial Testing Systems for Cohesionless Soils

The stress states and their changes that can be attained in the conventional triaxial testing method are reviewed and compared to those attained in other more sophisticated testing methods. These advanced tests have been developed to extend the ranges of the stress states and the changes in these states that can be controlled. In conventional triaxial testing on solid cylinder specimens σ₂′ is equal either to σ₁′ or to σ₃′ and only a jump rotation of 90° in the principal stress directions can be achieved. It is argued that in spite of this limitation the triaxial testing method is still a useful means to measure the strength and deformation characteristics of soils. The results, however, should be corrected to account for the actual states of stress in the field. Furthermore, some recent advances in the methods and equipment for triaxial testing and other related kinds of testing are reviewed with an emphasis on the importance of automation and simplification. Several examples are presented where automated controlled stress and/or strain path tests can be performed by means of a simple triaxial apparatus using various electronic transducers, microcomputers, and pneumatic pressurizing systems.