断层岩爆是应变局部化导致的系统失稳回跳

讨论了应变局部化、岩爆及Ⅱ类变形行为的关系，并利用梯度塑性理论得到了4种等效的回跳准则。局部化是岩爆的前兆之一，也是出现Ⅱ类变形行为的原因。利用最小势能原理及梯度塑性理论，可得到系统的失稳判据；利用位移法，可以得到系统的Ⅱ类变形行为。若非弹性剪切位移(或平均塑性剪切应变)的增加快于弹性剪切位移(或平均弹性剪切应变)的降低，将出现Ⅰ类变形行为；反之，将出现Ⅱ类变形行为。弹性区与剪切带宽度的比率越大，或剪切弹性模量与剪切降模量的比率越小，系统越容易失稳。

FAULT ROCKBURST I IS SNAP-BACK DUE TO SHEAR STRAIN LOCALIZATION

Four kinds of equivalent criteria of snap-back for the one-dimensional fault rockburst model under shear loading are proposed based on gradient-dependent plasticity. The relationship among rockburst,shear strain localization and snap-back (class II behavior) are discussed in detail. It is found that shear strain localization initiated at peak shear stress is a precursor of a rockburst and it is the reason for appearance of class II behavior. According to the minimum potential energy principle and the gradient-dependent plasticity,the instability criterion of the system composed of shear band and elastic rock mass outside the band can be derived theoretically. By using the displacement method,the total shear displacement can be divided into elastic part and plastic part,and the pastic shear displacement is dependent on the thickness of shear band. As a result,the condition of class II behavior of the system can be proposed. It is found from the study result that the condition of class II behavior is identical with the instability criterion of the system. If the plastic shear displacement along the tangential direction of fault band or average plastic shear strain increases faster than the elastic shear displacement or average elastic shear strain decreases,then the system shows class I behavior,otherwise it shows class II behavior. The instability criterion shows that the larger the ratio of elastic zone size to the thickness of the shear band is or the lower the ratio of the shearing elastic modulus to the shear softening modulus is,the more unstable the system is.