Abstract
The mechanical response and failure process of a jointed rock mass subjected to dynamic loading is very important for the safety and stability of rock engineering projects. In this study, we use RFPA2D-Dynamic, a rock dynamic failure process analysis platform, to establish a two-dimensional impact model of a jointed rock mass to analyze the mechanism of crack propagation in a jointed rock mass with preexisting cracks under dynamic loading. We discuss the influence of the stress wavelength and precrack inclination on the dynamic failure process and mode of the rock mass and compare this failure process with the failure model under static loading. The results show that the dynamic failure process and crack initiation type of a jointed rock mass are closely related to the stress wavelength. For a given peak, as the stress wavelength increases, the failure mode changes from local cracking that occurs above the precracks to a global instability caused by wing cracks. Meanwhile, as the wavelength increases, the shear cracks and mixed tensile-shear cracks generated at the two ends of the precracks are replaced by tensile cracks. The precrack inclination on a jointed rock mass mainly affects the strength of the jointed rock mass and the final failure mode. Specifically, when the joint inclination is small, the rock mass is severely damaged in the region above the precracks because the stress wave forms a region of cracks with a concentrated distribution. As the joint inclination increases, the damaged region becomes larger while the rock mass is less prone to failure; the strength of the rock mass gradually increases, and the wing cracks produced at the two ends of precracks propagate toward the upper and lower ends of the rock mass. However, when the stress wavelength is small, the precracks of different inclinations form cracks in the region above the precracks with a length similar to the precracks. For this condition, the propagation of the cracks is mainly controlled by the stress wavelength, while the influence of the inclination of the precracks is not significant. There is a significant difference between the failure modes of a rock specimen under dynamic loading or static loading because the stress wave produces a reflected tension wave in the direction parallel to the wave attack of the joint plane, which leads to spalling, while the wing cracks are more likely to occur under static loading.
Highlights
Because the jointed rock mass is a type of nonhomogeneous material, its failure process relies on the stress wavelength but is related to the distribution of its internal joints [1, 2]. erefore, studying the patterns of crack propagation of a jointed rock mass with different wavelengths and precrack inclinations has both theoretical significance and engineering value
Influence of the Stress Wavelength on the Type of Cracks. e cracks produced around the precrack in the rock specimen under dynamic loading have different types of generated cracks for different wavelengths
The crack type in the upper end of the precrack gradually evolves from a shear crack to a mixed tension-shear crack, and when stress wave IV is applied, the crack type completely evolves to a tensile crack
Summary
Because the jointed rock mass is a type of nonhomogeneous material, its failure process relies on the stress wavelength but is related to the distribution of its internal joints [1, 2]. erefore, studying the patterns of crack propagation of a jointed rock mass with different wavelengths and precrack inclinations has both theoretical significance and engineering value. Erefore, a systematic study of the mechanisms of crack initiation and propagation processes in rock masses under dynamic loading condition promises benefit in many areas from. Not so well understood is the dynamic failure process, which is closely related to crack behavior in terms of initiation, propagation and coalescence of cracks when the rock specimen is undertook different loading conditions. The effect of flaw dip angle on the dynamic failure processes is investigated by some researchers. The fracture effect of rock mass with a flaw dip angle of 45°–60° is the best In view of these arguments, further study of the effect of the flaw dip angle on the dynamic process in flawed specimen under a wide range of loading rates is essential to illuminate the relationship of these two factors. We discuss in depth the relationship between the influence of the stress wavelength on the type of initiation cracks and the influence of the wavelength and inclination on the mode of crack propagation, providing a reference for the design of relevant rock mass engineering projects
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