For heterogeneous rock specimen with smooth ends and with initially random material imperfections in uniaxial plane strain compression, the effects of pore pressure on the failure process and axially deformational characteristic are numerically modeled using FLAC in which the presence of pore pressure in a zone is taken into account by the incorporation of an effective stress. A FISH function is generated to prescribe the initial imperfections within the specimen using Matlab. For intact rock exhibiting linear strain-softening behavior beyond the occurrence of failure and then ideal plastic behavior, the failure criterion is a composite Mohr-Coulomb criterion with tension cut-off. Initial imperfections undergo ideal plastic behavior beyond the failure point. As pore pressure increases, the material imperfections extend early, the yielded elements coalesce to form shorter cracks early, the inclined shear fracturing bands intersecting the specimen occur early, the number of yielded elements in tension in the final deformational stage increases, and the length of splitting cracks increases. For rock specimen without pore pressure, shear failure is the dominant failure mode, while for rock specimen subjected to a certain pore pressure, both shear failure and tensile failures occur. Higher pore pressure decreases the peak stress and residual stress.
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