残余强度阶段大理岩流变特性试验研究

Testing study of rheological characteristic of marble being in residual strength stage

锦屏二级水电站引水隧洞埋深大、地应力水平高,高应力状态下的大理岩具有明显的时效特性,工程部分岩体处于残余强度阶段,其流变特性对围岩长期稳定性具有显著影响。利用三轴压缩全过程试验获得进入残余强度阶段的大理岩试件,以此来模拟工程塑性区岩体,并对残余强度阶段的岩石试件进行不同围压下的三轴蠕变试验,系统研究残余强度阶段大理岩的蠕变特性及其长期强度。试验表明:残余强度阶段的大理岩具有明显的瞬时变形、减速蠕变和稳定蠕变特性;受内部大量破裂网格的影响,残余强度阶段岩体的瞬时应变和蠕变量较完整岩块有很大程度的提高;残余强度阶段大理岩的总蠕变量及蠕变速率均随偏应力的增大而增大;长期强度小于其残余强度且随围压的增大而增大;试件长期抗剪强度不具有黏聚力,内摩擦角较残余内摩擦角有所提高。基于残余强度阶段大理岩的蠕变特性,采用Burgers模型模拟其蠕变过程,并对蠕变参数进行辨识,研究表明:Burgers模型模拟结果与蠕变试验具有很高的吻合度,能很好地反映残余强度阶段大理岩的流变特性;其流变参数中弹性模量EM和黏性系数ηM均随着偏应力的增大而减小,黏弹性剪切模量GK与黏弹性系数ηK随偏应力的增大先增大后减小。

The diversion tunnel of Jinping II hydropower station contains marble and has large burial depth and high geostress, which give rise to the marble has prominent rheological phenomenon. Part of the engineering rock mass is in residual strength stage, so it is significant to understand the rheological characteristic of marble being in residual strength stage. Triaxial creep tests were carried out for the marble samples which had experienced triaxial compressive full tests. Based on the tests, the creep characteristic and long-term strength of the marble being in residual strength stage were systematically discussed. The study showed that the marble has transient deformation, decelerating creep stag and steady-state creep stage with different confining pressure. Attribute to a plenty of fractures, for the marble being in residual strength stage, the capacity of transient deformation and creep deformation is heavy stronger than that of the intact marble. The whole creep deformation and the steady creep speed increase with deviatoric stress. Furthermore, long-term strength of marble, less than instantaneous strength,improve when confining pressure increasing. Due to the weakening in the creep process, the samples mostly do not have cohesion and the frictional angle enhance, compared with the samples which had gone through triaxial compressive full tests but not creep tests. Therefore, it is reasonable to disregard the cohesion in significant engineering. Eventually, based on the creep characteristics of the marble, the Burgers model was treated as theoretical model to fit the processed creep curves, the parameters were obtained by Levenberg-Marquardt algorithm. At the same time, the evolution of the parameters of the Burgers model also were discussed. The research showed that the Burgers model has a perfect agreement with experiment data, which fully reflects the rheological characteristic of the marble being in residual strength stage. Moreover, for the marble being in residual strength stage, the parameters of the Burgers model exhibit the characters of nonlinear. With the deviatoric stress increasing, elastic modulus EM and viscous coefficient ηM decrease and viscoelastic shear modulus GK and viscoelastic coefficient ηK increase at first and then decrease.