  To avoid the impact of inherent natural imperfections on experimental
outcomes during testing, a recently designed genuine triaxial apparatus has
enabled the replication of conditions where the three principal stresses
exhibit varying magnitudes. This setup facilitates the examination of fracture
behaviors in materials similar to the 4-series under genuine triaxial stress
states. The experimental findings revealed that the maximum strength
experiences significant influence from the minimum principal stress and the
intermediate principal stress in genuine triaxial stress conditions.
Specifically, for a fixed minimum principal stress ({\sigma}3), there is a
progressive reduction in peak strain as the intermediate principal stress
({\sigma}2) increases. Moreover, as the minimum principal stress ({\sigma}3)
rises, the magnitude of peak strain diminishes. The Young's modulus of the
specimens exhibits an exponential increase with the augmentation of confining
pressure, and it demonstrates a linear growth pattern as the intermediate
principal stress increases. Additionally, the cohesion force is observed to
rise while the internal friction angle decreases with the elevation of the
intermediate principal stress. The failure modes of the specimens in genuine
triaxial stress conditions can be categorized into three types, all of which
exhibit a specific angle between the fracture surface and {\sigma}3, ranging
from 50 to 62 degrees. Furthermore, a comparison between the computed range and
the actual measurement range of the fracture angle highlights several
limitations in the relationship between the fracture angle ({\theta}) and the
internal friction angle ({\phi}) within the Coulomb criterion, particularly in
rocks containing complex fracture systems.
