弹性模量对岩样破坏前兆及全部变形特征的影响

利用FLAC内嵌语言编制的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，计算了弹性模量不同时单缺陷岩样的全部变形特征，研究了弹性模量对岩样的破坏过程及前兆的影响。在峰前及峰后，岩石的本构模型分别取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。当弹性模量不是较高时，岩样自始至终仅出现一条倾斜的剪切带。当弹模较高时，最终剪切应变仅强烈集中于贯通岩样的剪切带内部。剪切带倾角在Arthur与Coulomb倾角之间，且随弹模的增加而降低，经典理论对此不能解释。随着弹模的增加，峰值应力增加，峰前的应力-轴向应变曲线变得陡峭，峰后的应力-轴向应变曲线的斜率几乎不变。随着弹模的增加，峰值强度所对应的轴向应变及侧向应变的大小均降低；应力-侧向应变曲线软化段变得陡峭。随着弹模的降低，侧向应变-轴向应变曲线、泊松比-轴向应变曲线及体积应变-轴向应变曲线在峰前发生转折（偏离线性状态）的程度越来越大；非弹性轴向应变增加；材料缺陷附近的最大剪切应变增量增加。岩样破坏的前兆随着弹性模量的降低而逐渐增强。

Effect of elastic modulus on precursor to failure and entire deformational characteristics of rock specimen

Using FISH functions written in FLAC, the axial, lateral and volumetric strains as well as the Poisson’s ratio of rock specimen with a material imperfection in plane strain compression were calculated at different elastic moduli. The influence of elastic modulus on failure process and precursor of the specimen was modeled. In elastic stage, the adopted constitutive relation of rock 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. If elastic modulus is not very high, only an inclined shear band is formed all along. For very high elastic modulus, finally, the intense shear strain is concentrated into a shear band bisecting the specimen. The numerically predicted shear band’s inclination angles approach Arthur’s and Coulomb’s inclinations and decrease with an increase of elastic modulus, as cannot be explained by the classical theories. With an increase of elastic modulus, the peak stress increases and the pre-peak stress-axial strain curve becomes steep, while the post-peak slope of stress-axial strain curve does not change. The absolute values of axial strain and lateral strain, which correspond to the peak stress, decrease and the post-peak stress-lateral strain curve becomes steep with an increase of elastic modulus. The decrease of elastic modulus leads to greater deviations of lateral strain-axial strain curve, Poisson’s ratio-axial strain curve and volumetric strain-axial strain curve from linear states; higher non-elastic axial strain and higher maximum shear strain increment in the vicinity of material imperfection. Therefore, the precursor to failure is more apparent at lower elastic modulus.