孔隙压力对含随机缺陷岩石破坏过程及全部变形特征的影响

对于平面应变压缩条件下含有随机缺陷的岩样,利用FLAC研究了孔隙压力对岩样破坏过程、全部变形特征及前兆的影响。以前编写的若干FISH函数,被用于生成缺陷和计算轴向、侧向、体积应变及侧向应变与轴向应变比值的负值(计算得到的泊松比)。在峰值应力之后,密实岩石单元服从线性应变软化行为及随后的理想塑性行为,而材料缺陷呈现理想塑性行为。当孔隙压力较高时,应力—侧向应变曲线具有一平台;破坏的前兆更明显;变形后岩样的体积总是大于原始体积;在初始加载阶段、均匀变形阶段及峰后变形阶段,由于明显的侧向膨胀,计算得到的泊松比远大于0.5。当孔隙压力较低时,在峰值应力之前,变形后岩样的体积小于原始体积,体积扩容出现于峰值应力之后,引起了负的体积应变。利用广义虎克定律,解释了平面应变弹性状态下数值结果的合理性。对岩样进行带状区域扫描后,确认随机缺陷的初始分布与岩样的最终破坏形态紧密相关。

Effect of Pore Pressure on Failure Processes and Overall Deformational Characteristics of Rock Specimen with Random Defects

For a rock specimen with random defects in uniaxial plane strain compression,the effects of pore pressure on the failure processes,overall deformational characteristics and precursors are numerically modeled using FLAC.FISH functions are used to generate defects and to calculate the lateral and volumetric strains as well as the ratio of negative lateral strain to axial strain(called the calculated Poisson′s ratio).At post-peak,intact rock elements are assigned to obey linear strain-softening behavior and later ideal plastic behavior,while material defects exhibit ideal plastic behavior.At higher pore pressures,the stress vs.lateral strain curve has a wider plateau;the precursors are more apparent;the deformed specimen volume is always larger than the original volume;the calculated Poisson's ratio in the initially loading stage,uniformly deformational stage and post-peak deformational stage is greatly higher than 0.5 owing to the apparent lateral expansion.At lower pore pressures,the deformed specimen is smaller than the undeformed specimen at pre-peak and the volume dilation occurs at post-peak,resulting in a negative volumetric strain.Using general Hooke's law,the reasonableness of the numerical results in plane strain elastic state is explained.The initial distribution of random defects is closely related to the final failure pattern of rock specimen,as is verified through scanning the specimen using an inclined zonal zone.