Numerical simulation of distributions of shear strain rate and displacements on free surfaces of three dimensional rock specimen in uniaxial compression

Previously numerical simulations of deformation and failure of rock specimen using Fast Lagrangian Analysis of Continua(FLAC) were mainly limited to plane strain condition different from the actual test condition of three-dimensional rock specimen in uniaxial compression.In the paper,three-dimensional rock specimen with rough ends was modeled by FLAC-3D.Distribution and evolution of shear strain rate,in-and off-plane displacements in free surfaces were investigated.Evolution of in-and off-plane displacements in vertical symmetrical axis of a free surface was monitored.In elastic stage,the adopted constitutive relation was linear elastic;in strain-softening stage,a composite Mohr-Coulomb criterion with tension cut-off was used and the post-peak constitutive relation was also linear.It was shown that uniform distribution of shear strain rate in free surfaces was changed to non-uniform state prior to peak stress.Symmetrical deformation mode of the specimen was converted into asymmetrical pattern beyond peak stress.Two spatial shear planes were found to be generated within specimen through analysis of the patterns of shear band on four free surfaces.One plane was superior to the others from the viewpoint of area of shear plane.Three-dimensional curved surfaces of in-and off-plane displacements were smooth and flat before losing of symmetry of deformation.Concavo-convex three-dimensional curved surfaces wee observed once the symmetry of deformation was violated.Positions where in-plane displacement changed remarkably corresponded to shear bands.Precursor to deformation and failure of the specimen could be identified form off-plane displacement in vertical symmetrical axis of a free surface since the separation of off-plane displacement-timestep curves occurred prior to peak stress.As timestep increased,three kinds of tendencies of off-plane displacement were observed in strain-softening stage.