Development of a True Triaxial Apparatus for Sands and Gravels

This paper presents a recently developed true triaxial apparatus and a series of verification studies. The apparatus is capable of handling 241-mm cubical specimens providing the means for testing specimens under a wide variety of stress paths under drained and undrained conditions. It uses flexible boundaries to apply three independently controlled principal stresses with back pressure. The apparatus also uses a fully computer-controlled electro-pneumatic loading system with advanced technology for data control. A testing program is presented for the purpose of verification. Pea-gravel specimens with D50=6.6 mm were tested under fully stress-controlled loading conditions. Stress paths used in this verification study include undrained and drained constant total mean stress paths and conventional triaxial compression and extension stress paths. Results from this study indicate that the newly developed apparatus is capable of capturing the stress-strain characteristics of coarse-grained soils.