ANALYSIS ON FAULT ROCKBURST CONSIDERING STRAIN RATE AND STRAIN GRADIENT
考虑应变率及应变梯度效应的断层岩爆分析

Dynamic shear instability of fault rockburst is analyzed with considering the effect of strain rate and interaction among microstructures. The second shear strain gradient and the function reflecting the effect of strain rate are introduced into the yield function of classical elastoplastic theory. The fault rockburst is simplified as the one-dimensional dynamic shear problem and shear localization is initiated at the peak shear stress. Symmetry of local plastic shear strain in shear band is considered and in the boundary of the band the strain is zero. In addition,the thickness of band is determined according to the maximum local plastic shear strain. Local plastic shear strain and local plastic shear displacement analytically obtained show that these two local parameters increase with strain rate. Beyond the peak shear stress,the structural response of the system composed of fault band and elastic rock outside the fault is proposed. If the post-peak stiffness of the structural response is infinity,the critical loading strain rate of rockburst can be deduced. Once the critical value is achieved,the rock burst occurs certainty. It is found that the critical parameter is dependent on both constitutive parameters of rock materials and the size of structure. Larger strain rate can lead to snap-back of instability of the system. Besides,if the effect of strain rate is neglected,the static results based on gradient-dependent plasticity by Wang et al. can be obtained by simplifying the present theoretical results.