STRENGTH AND DEFORMATION CHARACTERISTICS OF ROCK SAMPLE WITH DISCONTINUITIES UNDER NUMERICAL UNIAXIAL COMPRESSION SIMULATION TESTS

The discontinuities are the key factors that differentiate the rock mass and intact rock. The mechanical behaviours of rock mass are strongly affected by length, occurrence and consistency of the discontinuities. Characteristics-deformation, strength, failure modes of rock samples with various discontinuities under uniaxial compression have been studied based on the numerical modelling FLAC^3D.Rock samples with different groups of penetrated discontinuities and different unpenetrated discontinuities have been set up. On the basis of these models, a number of numerical uniaxial compression tests have been carried out, in which the shear and tensile strength criterion(Mohr-Coulomb criterion) has been used. During the uniaxial compression simulation tests, a servo-control program is used to restrict the maximum unbalanced force through adjusting the applied velocity. The results of simulation tests are shown as follow: rock samples with fewer than 4 groups of penetrated discontinuities are anisotropic while those with 4 groups of penetrated discontinuities are nearly isotropic. The deformation and strength parameters get lower as the number of penetrated discontinuities get higher in rock sample with same size. Stress drop is observed after peak stress in the stress-strain curve of rock sample with unpenetrated continuity. Uniaxial compressive strength derived from simulation is different from that calculated by analytic method based on shear strength and damage theory, which indicates that shear strength criterion may be not suitable for rock mass with unpenetrated discontinuities. The deformation and strength parameters get lower as the continuity trace length bigger. The failure modes of rock samples with discontinuities can be divided into three types: discontinuity-controlled, discontinuity-half controlled and discontinuity-uncontrolled. As the number of groups increases the failure are more likely to be discontinuity-controlled.