Deformation characteristics under confined triaxial extension stress

To investigate deformation characteristics under different stress states and loading paths, we conducted a true triaxial compression test using a rectangular specimen of 35 x 35 x 70 mm, a confined triaxial extension test and a confined triaxial compression test using a cylindrical specimen of phi 50 x 100 mm. We also investigated the differences in boundary conditions between fluid pressure and solid piston pressure, during sigma 1 = sigma 2 loading. The true triaxial test is superior in obtaining continuous deformation behaviors from ductile under a compression regime to brittle under an extension regime. The maximum principal stress increased by a finite amount in changing from a compression state to an extension state. The brittleness is defined as the reduction in the maximum principal strain observed under increases in the intermediate principal stress. Transition deformation characteristics are also observed when changing from a compression state to an extension state.