| The problem of rock dynamic damage is encountered in the process of underground cavern excavation. How to guarantee the stability of surrounding rocks depends on the in-depth research of the dynamic properties of rocks and surrounding rock failure mode in the process of stress adjustment. It is an important research method to analyze characteristics of stress wave signal in the process of rock damage. This paper proposes the Fourier transform, short-time Fourier transform as well as wavelet transform to analyze the time-frequency characteristics of the stress wave and energy characteristics. A model is established by utilizing numerical simulation methods, which elaborates the impact mechanism of blasting load on the underground cavern. And the propagation characteristics and the law of stress wave in rock mass are analyzed respectively from the particle velocity, amplitude and the maximum stress. The spectral characteristics of seismic stress wave are analyzed by combing with underground caverns micro seismic monitoring. A stability evaluation method is put forward of underground cavern based on micro seismic dynamic analysis. The main research conclusions are as follows:(1) In the process of the underground space excavation, stress wave signals in the rock are monitored which results from direct human activities, such as artificial tapping, drilling, blasting, rock failure and fault rupture producing micro vibration. All of these micro vibrations can be analyzed by the Fourier transform, short-time Fourier transform and wavelet transform.(2) Depending on the analysis of vibration frequency of micro seismic signal and blasting signal, it shows that micro seismic signal generally has one main frequency. However, blasting signal always has multiple main frequency. The reason may lies in that millisecond blasting produces multiple frequency in the process of excavation. Based on their energy distribution, the energy of the micro vibration signal and blasting vibration signal basically concentrate in low frequency band. However, blasting signal gathers certain energy in high frequency band. Compared to the micro seismic signal, its energy distribution is wider.(3) Through numerical simulation of the underground cavern blasting construction, we can find the surrounding rock particle vibration velocity and vibration amplitude are skirting the largest, followed by the side walls, vaults minimum. Velocity in the horizontal direction is the vertical direction speed several times. The foundation from the explosion source greatest and impact action by the most intense. Because the geometry of the vault location and the stress wave reflection superposition and attenuation, making stress wave and displacement generated will be minimized. From the spectrum, differential blasting have multiple main frequency about80Hz-250Hz, and the maximum main frequency of about130Hz, which is consistent with the blasting signal monitored.(4) Through the Dagangshan hydropower station micro seismic monitoring events and stress wave analysis, with sub-steps to carry out the construction from top to bottom, the lower cavern excavation micro seismic events due to blasting influence gradually increased, and a larger magnitude micro seismic in vaults and walls on both sides of micro seismic vibrations are relatively small. Through comprehensive analysis of micro seismic monitoring data, stability evaluation method is proposed based on dynamics analysis of seismic time-space distribution, magnitude and energy distribution underground cavern.Using the large amount of rock mass state information contained in the stress wave during the rock mass dynamic failure process to feedback the dynamic damage process of rock mass, thereby distinguish the stability of underground caverns and choose thesupport way for underground caverns. It provides a strong theoretical and practical foundation for underground engineering design and construction.
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