Effect of height of rock specimen on strain localization, precursor to failure and entire deformational characteristics

Patterns of shear band,precursors to shear failure occurring instrain-softening stage,axial,lateral and volumetric strains as well as Poisson's ratio ofplane strain rock specimens in compression for different heights were investigated byuse of Fast Lagrangian Analysis of Continua(FLAC).A material imperfection closer tothe lower-left comer of the specimen was prescribed.For finer mesh,the imperfectionwas modeled by four null elements,while it was modeled by a null element for coarsermesh.FISH functions were written to calculate the entire deformational characteristics ofthe specimen.In elastic stage,the adopted constitutive relation was linear elastic;instrain-softening stage,a composite Mohr-Coulomb criterion with tension cut-off and apost-peak linear constitutive relation were adopted.Height of rock specimen does not in-fluence shear band's pattern(including the thickness and inclination angle of shearband).The slopes of the post-peak stress-axial strain curve,stress-lateral strain curve,lateral strain-axial strain curve,Poisson's ratio-axial strain curve and volumetricstrain-axial strain curve depend on the height.Hence,the slopes of these curves cannotbe considered as material properties.Nonlinear deformation prior to the peak stress is akind of precursors to shear failure,which is less apparent for shorter specimen.For thesame axial strain,lower lateral expansion is reached for shorter specimen,leading tolower Poisson's ratio and higher volumetric strain.The maximum volumetric strain oflonger specimen is less than that of shorter specimen.The conclusions drawn from nu-merical results using finer mesh qualitatively agree with those using coarser mesh.

Patterns of shear band, precursors to shear failure occurring in strain-softening stage, axial, lateral and volumetric strains as well as Poisson＇s ratio of plane strain rock specimens in compression for different heights were investigated by use of Fast Lagrangian Analysis of Continua（FLAC）. A material imperfection closer to the lower-left corner of the specimen was prescribed. For finer mesh, the imperfection was modeled by four null elements, while it was modeled by a null element for coarser mesh. FISH functions were written to calculate the entire deformational characteristics of the specimen. In elastic stage, the adopted constitutive relation was linear elastic; in strain-softening stage, a composite Mohr-Coulomb criterion with tension cut-off and a post-peak linear constitutive relation were adopted. Height of rock specimen does not influence shear band＇s pattern （including the thickness and inclination angle of shear band）. The slopes of the post-peak stress-axial strain curve, stress-lateral strain curve, lateral strain-axial strain curve, Poisson＇s ratio-axial strain curve and volumetric strain-axial strain curve depend on the height. Hence, the slopes of these curves cannot be considered as material properties. Nonlinear deformation prior to the peak stress is a kind of precursors to shear failure, which is less apparent for shorter specimen. For the same axial strain, lower lateral expansion is reached for shorter specimen, leading to lower Poisson＇s ratio and higher volumetric strain. The maximum volumetric strain of longer specimen is less than that of shorter specimen. The conclusions drawn from numerical results using finer mesh qualitatively agree with those using coarser mesh.