EFFECTS OF STRAIN-SOFTENING DILATANCY ON PROGRESSIVE DEFORMATIONS AND PRECURSORS TO FAILURE OF ROCK WITH INITIAL RANDOM IMPERFECTIONS

For rock specimens with initially random material imperfections in uniaxial plane strain compression, the effects of shear dilatancy on the failure precursors and deformational characteristics are modeled using FLAC.For compact rock elements exhibiting the linear strain-softening behavior after the occurrence of failure and then the ideal plastic behavior, the failure criterion is a composite MohrCoulomb criterion with tension cut-off.Imperfections undergo an ideal plastic behavior after the occurrence of failure.As axial strain increases, the number of failed elements inside the specimen increases till a constant, which increases with increasing dilation angle, is reached.At a much higher dilation angle, the calculated Poisson's ratio at the pre-peak time can be higher than 0.5;shear dilatancy occurs at the pre-peak time; the final volume of the deformed rock specimen is higher than the original volume.Shear strain localization leading to a relative sliding between adjacent blocks and shear dilatancy in shear bands are responsible for the volume dilation of the rock specimen with non-zero dilation angles.Rock specimens with higher dilation angles have more apparent precursors to failure through observing the shear strain increment and the number of failed elements at peak stress as well as the deviations of lateral strain, calculated Poisson's ratio and volumetric strain at the pre-peak time from linear states.The measured well-developed shear band inclination in the interior of rock specimens is closer to the Arthur theory and more scattered owing to the curved shear bands at lower dilation angles.