Brittle-ductile transition and failure mechanism of Jinping marble under true triaxial compression

The research was focused on the execution of true triaxial compression tests and adopted acoustic emission (AE) and scanning electron microscopy (SEM). By doing so, the authors investigated the strength, deformation, AE, macroscopic and microscopic failure characteristics of Jinping marble in the 3-d stress space during brittle-ductile failure. The results showed that under true triaxial compression, when ductile failure occurs in Jinping marble, some ductile deformation remained in the samples, even after reaching peak strength. Post-peak ductility indicates Jinping marble with a certain post-peak carrying capacity, which has an important effect on rock failure. Moreover, the magnitude of the intermediate principal stress and the minimum principal stress affect the brittle-ductile transition and failure mechanism of Jinping marble. When the minimum principal stress is small, rocks present brittle failure and split to an extent that mainly depends on tensile failure, and the brittle-ductile transition of rocks is only slightly influenced by the intermediate principal stress. Under large minimum principal stress conditions, the rock behavior gradually turns from ductile to brittle failure with increasing intermediate principal stress. When the minimum principal stress is large and the intermediate principal stress is small, rocks exhibit ductile failure (mostly shown as shear failure). Besides, when the minimum principal stress is large and the difference between minimum and intermediate principal stress is larger, brittle failure occurs along tensile-shear fractures.