加载速度对断层-围岩系统变形及快速回跳的影响

在平面应变状态下，采用拉格朗日元法模拟了加载速度对断层-围岩系统形成时的应力水平、塑性区尺寸及剪切带图案、系统的最大承载能力以及快速回跳发生时的应力水平的影响。在数值计算中，采用了莫尔-库仑与拉破坏复合的破坏准则。峰后岩石的本构关系为线性应变软化。通常断层带-围岩系统形成之后系统的承载能力达到最大，之后系统的承载能力开始下降处于应变软化状态。当位于试样加载端上的单元的压缩应力-压缩位移曲线的峰后刚度足够大时，系统就会发生弹性回跳现象，即失稳破坏。随着加载速度的增加，断层带-围岩系统形成时的应力水平、断层带-围岩系统的最大承载能力、快速回跳发生时的应力水平及上述三者所对应的加载端部位移都增加，屈服单元数目增多，塑性区域不再保持平直，这都将大大增加系统的变形阻力。当加载速度较大时，较高的剪切应变率集中在断层带位置及断层带之外的弹性体的某些区域都是可能的。

Numerical simulation of influence of loading rate on deformation characteristics and snap-back for fault band and elastic rock system

Influences of loading rate on the stress level when a system composed of fault band and elastic rock was formed,the size of plastic zones,the patterns of localized shear band,the maximum load-carrying capability of the system,and on the stress level when the snap-back of the system occurred were modeled numerically by FLAC(Fast Lagrangian Analysis of Continua).The adopted failure criterion was a composite Mohr-Coulomb criterion with tension cut-off;and a linear strain-softening post-peak constitutive relation of rock was adopted.In general,after fault band-elastic body system is generated,the load-carrying capability of the system reaches its maximum value.Thereafter,it begins to decrease so that the system is in strain-softening stage.If the post-peak stiffness of compressive stress-compressive displacement curve for the monitored element at loading end of plane strain specimen is high enough,the snap-back(unstable failure) of the system occurs.As loading rate increases,the stress level corresponding to the formation of the system and the corresponding displacement increase;the maximum load-carrying capability of the system and the corresponding displacement increase;the stress level when the snap-back of the system occurs and the corresponding displacement increase.As loading rate increases,the number of yielded elements increases and the thickness of fault band no loner remains a constant,leading to an increase in deformation resistant of the system.For higher loading rate,it is possible that higher shear strain rates are concentrated into both fault band and some elements remaining elastic outside the band.