泊松比对岩样破坏模式及全部变形特征的影响

EFFECTS OF POISSON'S RATIO ON FAILURE MODE AND OVERALL DEFORMATIONAL CHARACTERISTICS OF A ROCK SPECIMEN

利用编写的计算岩样全部变形特征的FISH函数,采用FLAC模拟了泊松比不同时单缺陷岩石试样的破坏及全部变形特征。在峰前及峰后,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。高泊松比使岩样发生由单一剪切破坏向复杂破坏转变、破坏区域的面积增加、剪切带倾角降低,Coulomb、Roscoe及Arthur理论对此无法解释。不同泊松比时计算得到的峰前应力-轴向应变曲线、应力-侧向应变曲线、侧向应变-轴向应变曲线、体积应变-轴向应变曲线的线性阶段与平面应变压缩条件下的线弹性解吻合。若泊松比超过1/3,通过计算得到的平面应变压缩泊松比可大于0.5,这被数值模拟确认。泊松比的增加使峰后的侧向应变-轴向应变曲线、体积应变-轴向应变曲线、计算得到的泊松比-轴向应变曲线变得不陡峭,使峰后的应力-侧向应变曲线变得陡峭,使破坏的前兆变得不明显。

Using FISH functions written in FLAC to calculate the overall deformational characteristics, the effects of Poisson＇s ratio in the elastic stage on the failure mode and overall deformational characteristics were modeled for a rock specimen with a material imperfection in plane strain compression. In the elastic stage, the adopted constitutive relation of rock was linear elastic; and in the strainsoftening stage, a composite Mohr-Coulomb criterion with tension cut-off was used and the post-peak constitutive relation was also linear. The increased Poisson＇s ratio in the elastic stage leads to a transition of failure mode from single to complex shear fractures and a larger failed area is expected. The predicted shear band inclination is lower at a higher Poisson＇s ratio in the elastic stage, which cannot be explained by Coulomb, Roscoe and Arthur theories. Prior to the peak stress, the calculated slopes of the linear stress-axial strain curves, stress-lateral strain curves, lateral strain-axial strain curves and volumetric strain-axial strain curves at different Poisson＇s ratios in the elastic stage are consistent with the linear elastic solutions in plane strain compression. The calculated Poisson＇s ratio in plane strain compression is higher than 0.5 if the adopted Poisson＇s ratio in the elastic stage exceeds 1/3, as is confirmed by the present numerical simulation. At a higher Poisson＇s ratio in the elastic stage, the post-peak lateral strain-axial strain curve, volumetric strain-axial strain curve and calculated Poisson＇s ratio-axial strain curve become less steep; whereas the post-peak stress-lateral strain curve becomes steep and the precursor to failure is less apparent.