剪胀对岩样全部变形特征的影响

Effects of Shear Dilatancy on Entire Deformational Characteristics of Rock Specimen

采用FLAC内嵌语言FISH编制了计算平面应变压缩岩样轴向、侧向、体积应变及泊松比的FISH函数,研究了剪切扩容对剪切带图案及岩样全部变形特征的影响。在峰值强度之前及之后,岩石的本构模型分别取为线弹性及莫尔库仑剪破坏与拉破坏复合的应变软化模型。分析表明,增加剪胀角使岩样由单一向共轭剪切破坏转变,并使接近Arthur倾角的剪切带倾角增加。剪切带宽度随剪胀角增加,可由基于梯度塑性理论且考虑剪胀后的剪切带宽度公式进行解释。剪胀角增加导致峰值强度及对应的轴向、侧向及体积应变增加。在峰后,由于剪胀引起剪切带条数及宽度增加,因而,轴向应力-轴向及侧向应变曲线软化段都变平缓。剪胀角较高时,岩样可获得更大的侧向变形量及泊松比,甚至是负的体积应变;岩样失稳破坏的前兆更加明显。

FISH functions are written and embedded in FLAC to calculate axial, lateral and volumetric strains as well as Poisson＇s ratio for rock specimen in plane strain compression. Influences of shear dilatancy on shear band （SB） patterns and entire deformational characteristics of the specimen are investigated numerically. In elastic stage, the adopted constitutive relation of rock is linear elastic; in strain-softening stage, a composite Molar-Coulomb criterion with tension cut-off is used and the post-peak constitutive relation is linear. It is shown that increase of dilation angle leads to 1） transition of failure mode from a single to conjugate SBs; 2） increase of SB＇ s inclination closer to Arthur＇ s theory; 3） increase of SB＇ s thickness, as qualitatively agrees with the formula considering shear dilatancy based on gradient-dependent plasticity ; 4） increase of peak strength and corresponding axial, lateral and volumetric strains ; 5） no steeper axial stress-axial strain curve and axial stress-lateral strain curve beyond the peak since SB＇ s number and thickness increase with dilation angle based on analytical solutions applicable to uniaxial compression of rock specimen; 6） higher lateral deformation and Poisson＇s ratio, and even negative volumetric strain; and 7） more apparent precursor to instability failure of rock specimen.