岩样尺度、孔道及端部摩擦效应的数值分析

NUMERICAL ANALYSIS OF SIZE SCALE,INNER HOLE AND END RESTRAINT EFFECTS OF ROCK SAMPLES

采用FLAC3D分析岩性参数、软化方法、网格划分和加载速率对圆柱岩样单轴压缩应力-应变曲线的影响,并基于优化参数分析岩样尺度、孔道及端部摩擦效应。当峰后软化模量增加、剪胀角增大、抗拉强度降低、单元划分变细或加载速率减小时,轴向应力-应变曲线的峰后软化段趋于陡峭。在单轴压缩时,端部光滑岩样一端产生Λ形破坏带,长径比对强度无明显影响;端部固定且长径比大于2时,岩样在中部产生X形破坏带,其峰值强度大于端部光滑岩样,且随长径比变化不大;端部固定且长径比小于2时,强度和平均模量随长径比减小而增大。孔道岩样的平均模量与孔径无明显关系;在相同围压下强度随着孔径增大而降低,峰后软化曲线趋于陡峭。完整和中空岩样的破坏均从岩样中心逐步向周边扩展,中空岩样形成2个同顶点圆锥面破坏带。数值模拟与试验结果比较吻合,可用于相关岩体工程设计和分析。

The influences of mechanical parameters of rock mass,strain-softening methods,mesh density and loading rate on stress-strain curves are analyzed with FLAC^3D.Size scale,inner hole and end restraint effects are then studied based on optimized parameters.When post-peak softening modulus,dilation angle or mesh number increase,tensile strength or loading rate decreases,and softening section of uniaxial compressive stress-strain curves becomes sharper.A Λ-shaped failure form is generated near one end of the sample,and slenderness ratio has no obvious effect on strength when ends are free.For fixed-end sample,an X-shaped shear band is created in the middle part,and the strength is larger than that of free-end sample under the same confining pressure;however,the strength doesn＇t vary with slenderness ratio when slenderness ratio is greater than 2.On the contrary,both strength and average modulus decrease with slenderness ratio when the latter is less than 2.When the diameter of inner hole increases,average modulus has no obvious change,strength under the same confining pressure increases,and softening section of post-peak curve becomes steeper.The yield zones of intact sample and the hollow one propagate both from the centre to the side of the cylinder sample,and yield surfaces like two cones with the same peak value are formed in hollow sample ultimately.Simulated and test results agree with each other well,and this approach could be used for design and analysis of rock mass engineering.