For a rock specimen with random defects in uniaxial plane strain compression

the effects of pore pressure on the failure processes

overall deformational characteristics and precursors are numerically modeled using FLAC.FISH functions are used to generate defects and to calculate the lateral and volumetric strains as well as the ratio of negative lateral strain to axial strain（called the calculated Poisson′s ratio）.At post-peak

intact rock elements are assigned to obey linear strain-softening behavior and later ideal plastic behavior

while material defects exhibit ideal plastic behavior.At higher pore pressures

the stress vs.lateral strain curve has a wider plateau;the precursors are more apparent;the deformed specimen volume is always larger than the original volume;the calculated Poisson’s ratio in the initially loading stage

uniformly deformational stage and post-peak deformational stage is greatly higher than 0.5 owing to the apparent lateral expansion.At lower pore pressures

the deformed specimen is smaller than the undeformed specimen at pre-peak and the volume dilation occurs at post-peak

resulting in a negative volumetric strain.Using general Hooke’s law

the reasonableness of the numerical results in plane strain elastic state is explained.The initial distribution of random defects is closely related to the final failure pattern of rock specimen

as is verified through scanning the specimen using an inclined zonal zone.