Abstract: 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.

Key words: rock mechanics, fault band and elastic rock system, strain-softening, load-carrying capacity, plane strain, snap-back, unstable failure