Effect of softening modulus on entire deformational characteristics of rock specimen

FISH functions were written to calculate axial,lateral and volumetric strains as well as Poisson’s ratio of rock specimen in plane strain compression.Influence of softening modulus on shear band(SB) patterns and entire deformational characteristics of the specimen was investigated by use of FLAC.In elastic and strain-softening stages,the linear elastic and linear strain-softening constitutive relations were adopted,respectively.Mohr-Coulomb criterion with tension cut-off was used beyond the elastic state.Numerical results showed that the increase of the softening modulus led to 1) transition of SB inclination from Arthur’s inclination to Coulomb’s inclination,which could not be explained by Coulomb,Roscoe,and Arthur’s inclinations,possibly due to neglecting the progressive failure of rock;2) decrease of SB’s thickness that could be qualitatively explained by the theoretical expression considering shear dilatancy based on gradient-dependent plasticity;3) increase of the minmum volume that the specimen in compression could obtain;4) more apparent precursor to unstable failure of the specimen;5) slightly steeper post-peak axial stress-axial strain curve,the axial stress-lateral strain curve,the lateral strain-axial strain curve,the Poisson’s ratio-axial strain curve and the volumetric strain-axial strain curve.Reasonableness of the former two numerical results was qualitatively explained by the previous analytical solutions in uniaxial compression of rock specimen subjected to shear failure.