INFLUENCE OF STRENGTH PARAMETERS ON OVERALL DEFORMATIONS OF ROCK SPECIMENS WITH INITIALLY RANDOM MATERIAL IMPERFECTIONS
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摘要: 在单轴平面应变压缩条件下, 采用FLAC模拟了初始内聚力及内摩擦角对具有随机材料缺陷岩样轴向、侧向、体积变形及由侧向应变及轴向应变计算得到的泊松比的演变的影响。采用编写的FISH函数于试样内部规定随机缺陷并计算其全部变形特征。密实的岩石服从莫尔库仑剪破坏与拉破坏复合的破坏准则, 破坏之后呈现应变软化—理想塑性行为。随着强度参数(初始内聚力及内摩擦角)的增加, 应力峰值及对应的侧向应变的值提高, 体积应变的峰值增加, 应力峰值所对应的计算得到的泊松比稍有增加。由于被剪切带所分割的毗邻块体之间的相对滑动, 纵然扩容角为零, 试样在峰后的变形阶段, 仍然可以观察到体积膨胀现象, 这与作者的理论分析结果一致。当强度参数降低时, 侧向应变—轴向应变曲线、体积应变—轴向应变曲线及计算得到的泊松比—轴向应变曲线的峰前非线性部分变得短暂。剪切带倾角的数值解的上限低于Coulomb理论, 下限在Roscoe理论附近波动, Arthur理论的预测结果与本文剪切带倾角的数值解更接近.Abstract: For heterogeneous rock specimen with smooth ends and initially random material imperfections in uniaxial plane strain compression, the effects of initial cohesion and internal friction angle on the overall deformational characteristics (such as the axial, lateral and volumetric strains as well as the calculated Poisson's ratios) are modeled using FLAC. A few written FISH functions are used to set the random imperfections and to calculate the overall deformational characteristics. For intact rock, the failure criterion is a combined Mohr-Coulomb criterion with tension cut-off, exhibiting linear strain-softening and then ideal plastic behavior beyond the occurrence of failure. Imperfection undergoes ideal plastic behavior beyond the occurrence of failure. As strength parameters (such as initial cohesion and internal friction angle) increase, the peak stress and related lateral strain increase, and the peak volumetric strain increases also, and the calculated Poisson's ratio corresponding to the peak stress increases slightly. At post-deformational stage, the volume of the specimen can dilate although the dilation angle is zero, as is in agreement with the analytical solution proposed by Wang (2006). This is attributable to the relative sliding between adjacent rock blocks separated by shear zones. With lower strength parameters, the nonlinear pre-peak portions of lateral strain-axial strain curve, volumetric strain-axial strain curve and calculated Poisson's ratio-axial strain curve become shorter. The numerically predicted upper bound of shear band inclination is lower than that predicted by Coulomb theory, and the lower bound approaches that predicted by Roscoe theory. The predicted results by Arthur theory are closer to the present numerical shear band inclination.
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Key words:
- cohesion /
- internal friction angle /
- lateral strain /
- volumetric strain /
- random imperfection /
- dilatancy
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图 2 不同强度参数时应力—轴向应变曲线
Figure 2. The stress-axial strain curves with different strength parameters
图 3 不同强度参数时应力—侧向应变曲线
Figure 3. The stress-lateral strain curves with different strength parameters
图 4 不同强度参数时侧向应变—轴向应变曲线
Figure 4. The lateral strain-axial strain curves with different strength parameters
图 5 不同强度参数时体积应变—轴向应变曲线
Figure 5. The volumetric strain-axial strain curves with different strength parameters
图 6 不同强度参数时计算得到的泊松比—轴向应变曲线
Figure 6. The calculated Poisson's ratio-axial strain curves with different strength parameters
图 7 不同强度参数时试样的最终破坏模式
Figure 7. The final failure modes of rock specimens with different strength parameters
图 8 不同强度参数时试样最终的变形后的剪切应变增量等值线图
Figure 8. The final deformed shear strain increment contour maps of final deformed rock specimens with different strength parameters
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