The deformation and fracture of rocks under combined stress states are most fundamental problems in rock mechanics. In previous works, however, the deformation, including the dilatancy, and fracture have been studied under the axi-symmetric stress state (σ1<σ2=σ3 or σ1=σ2>σ3). To discuss the deformation and fracture in actual cases, deformation experiments are needed under more general triaxial stress states (σ1>σ2>σ3).
Recent development of a new triaxial compression technique by Mogi (1971) has made it possible to study some deformational properties, such as fracture strength, yield stress, ductility, etc., under general triaxial stress states. In the preceding experiments, the three principal stresses and one of the principal strains were measured. In this paper, the measurements of all components of principal stresses and strains are reported for the first time. The deformational behavior of rocks under general triaxial stress states has been made clear. Particularly, the result shows that dilatancy is highly anisotropic under general triaxial stress states.
