Abstract: The rock vibrations caused by blasting excavation in deep caverns under high in-situ stress conditions include explosion seismic wave and seismic wave induced by rapid release of in-situ stress on the blasting excavation surface. There is no obvious demarcation point between these two types of waves in the time domain, which brings great inconvenience to study the vibration characteristics of explosion seismic wave and induced seismic wave and its surrounding rock dynamic response alone. In this study, the variational mode decomposition (VMD) is used for the first time to separate the explosion-induced seismic waves and the in-situ stress-related seismic waves for the rock vibrations measured in a typical deep cavern. The reliability of VMD in the separation is verified before the practical application. Based on the separation signals, the frequency characteristics and peak particle velocity (PPV) attenuation laws of the two waves are investigated. The results show that VMD method can adaptively determine the number of modal decomposition of the given signal and match the optimal center frequency and limited bandwidth of each modal component, which can effectively realize the separation of the two waves in deep cavern blasting excavation. The separation signals indicate that the center frequency of the in-situ stress-related seismic waves is significantly lower than that of the explosion-induced seismic waves. Due to the seismic waves caused by the rapid in-situ stress release, the total rock vibrations are increased significantly in the lower frequency components. Compared with the explosion-induced seismic waves, the in-situ stress-related seismic waves decay with distance at a slower rate and become the predominant vibration component in the middle and far fields.

Key words: deep cavern, blasting excavation, vibration, variational mode decomposition, center frequency