EFFECTS OF STRAIN-SOFTENING DILATANCY ON PROGRESSIVE DEFORMATIONS AND PRECURSORS TO FAILURE OF ROCK WITH INITIAL RANDOM IMPERFECTIONS
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摘要: 在单轴平面应变压缩条件下, 采用FLAC模拟了剪切扩容对含随机缺陷岩石破坏前兆及变形特征的影响。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。缺陷在破坏之后经历理想塑性行为。随着轴向应变的增加, 试样内部破坏的单元数目增加, 直到达到一个常数, 该常数随着扩容角的增加而增加。当扩容角较高时, 计算得到的泊松比在峰前就可以超过0.5;剪切扩容于峰前发生; 变形后试样的最终体积大于初始体积。剪切局部化(导致了毗邻块体之间的相对滑动)及剪切扩容(发生于剪切带内部)是非零扩容角试样峰后体积膨胀的原因。在峰前, 通过观察剪切应变增量、破坏的单元数目、侧向应变、计算得到的泊松比及体积应变可以发现, 扩容角越高, 试样破坏的前兆越明显。在低扩容角时, 由于弯曲的剪切带边界, 试样内部充分发展的剪切带的倾角比较分散, 剪切带的倾角更接近Arthur理论。Abstract: For rock specimens with initially random material imperfections in uniaxial plane strain compression, the effects of shear dilatancy on the failure precursors and deformational characteristics are modeled using FLAC.For compact rock elements exhibiting the linear strain-softening behavior after the occurrence of failure and then the ideal plastic behavior, the failure criterion is a composite MohrCoulomb criterion with tension cut-off.Imperfections undergo an ideal plastic behavior after the occurrence of failure.As axial strain increases, the number of failed elements inside the specimen increases till a constant, which increases with increasing dilation angle, is reached.At a much higher dilation angle, the calculated Poisson's ratio at the pre-peak time can be higher than 0.5;shear dilatancy occurs at the pre-peak time; the final volume of the deformed rock specimen is higher than the original volume.Shear strain localization leading to a relative sliding between adjacent blocks and shear dilatancy in shear bands are responsible for the volume dilation of the rock specimen with non-zero dilation angles.Rock specimens with higher dilation angles have more apparent precursors to failure through observing the shear strain increment and the number of failed elements at peak stress as well as the deviations of lateral strain, calculated Poisson's ratio and volumetric strain at the pre-peak time from linear states.The measured well-developed shear band inclination in the interior of rock specimens is closer to the Arthur theory and more scattered owing to the curved shear bands at lower dilation angles.
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Key words:
- shear dilatancy /
- random imperfection /
- shear band /
- volumetric strain /
- precursor
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图 1 含缺陷的岩样的边界条件
Figure 1. Model geometry and boundary conditions of a rock specimen with imperfections
图 2 扩容角对试样最终破坏形态的影响
Figure 2. Effects of the dilation angle on the final failure patterns of a specimen
图 3 扩容角对破坏单元数-轴向应变曲线的影响
Figure 3. Number of failed elements-axial strain curves at different dilation angles
图 4 扩容角对侧向应变-轴向应变曲线的影响
Figure 4. Lateral strain-axial strain curves at different dilation angles
图 5 扩容角对计算得到的泊松比-轴向应变曲线的影响
Figure 5. Calculated Poisson' s ratio-axial strain curves at different dilation angles
图 6 扩容角对体积应变-轴向应变曲线的影响
Figure 6. Volumetric strain-axial strain curves at different dilation angles
图 7 方案1至5的剪切应变增量等值线图(应变软化行为的开始时)
Figure 7. Shear strain contour diagrams for schemes 1 to 5 when strain-softening behavior just occurs
图 8 当时间步达到12000时方案1至5的剪切应变等值线图
Figure 8. Shear strain contour diagrams for schemes 1 to 5 at 12000 timesteps
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