软化模量对岩样全部变形特征的影响

Effect of softening modulus on entire deformational characteristics of rock specimen

采用FLAC内嵌语言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。研究了软化模量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为线弹性模型及莫尔–库仑剪破坏与拉破坏复合的应变软化模型。结果表明,随着软化模量(脆性)的增加,剪切带倾角由Arthur向Coulomb倾角转变,Coulomb、Roscoe及Arthur理论对此不能解释,可能是未考虑渐进破坏;剪切带宽度降低,这可采用基于梯度塑性理论且考虑剪胀的剪切带宽度的公式予以定性的解释;岩样可以达到的最小体积增加;岩样失稳破坏的前兆越来越明显;峰后的轴向应力–轴向应变曲线、轴向应力–侧向应变曲线、侧向应变–轴向应变曲线、泊松比–轴向应变曲线及体积应变–轴向应变曲线均有稍微变陡峭的趋势,可采用基于梯度塑性理论的单轴压缩岩样受到剪切破坏时的解析解对前2种曲线的数值解的合理性进行定性的解释。

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.