Abstract：As the confining stress is higher，rock mass strength is less anisotropic. On the basis of the friction criterion of rigid discontinuities in the rock mass and the Hoek-Brown strength criterion of rock mass，the critical confining pressure is deduced. When the confining pressure is larger than the critical value，the strength of the rock mass with rigid discontinuities would change from anisotropy to isotropy. The derivation results show that the critical confining pressure is mainly related to parameter m in Hoek-Brown strength criterion and the uniaxial compressive strength. Based on the existing tests，rock mass with continuities are modeled with FLAC3D. Then，the Hoek-Brown criterion and the critical confining pressure mentioned above are verified. The results show that the strength of rock mass with one group or two groups of rigid discontinuities is anisotropic when the confining stress is lower than the critical confining stress，but isotropic when the confining stress is higher than the critical confining stress. For the rock mass with three group of cracks，the real critical confining stress is smaller than expected due to the locking effect.
2013, Vol. 32 
