Meitan xuebao (May 2023)
Transmission model and propagation attenuation law of stress wave in gradient surrounding rock structure
Abstract
Rock bolt support and borehole pressure relief change the medium properties of roadway surrounding rock, form the roadway gradient surrounding rock structure with three media and two planes, increase the absorption and attenuation ability of stress waves, and prevent the impact damage of roadway. In order to reveal the attenuation law of stress wave propagation in roadway gradient surrounding rock structure, the stress wave transmission model of gradient surrounding rock structure is established, and the mechanism of energy absorption and burst prevention of gradient surrounding rock structure is revealed from the aspect of wave field decomposition and energy distribution of elastic wave at the interface of different medium. The influence of the density of relief zone and the incident angle of stress wave on the energy coefficient is analyzed. It is found that the density of relief zone and the incident angle of gradient surrounding rock can significantly affect the energy coefficient of each refraction wave. Based on the numerical calculation of different gradient surrounding rock structure, the influence law of gradient surrounding rock structure on stress wave propagation attenuation is analyzed by integrating the amplitude attenuation factor, wave impedance matching factor, energy absorption ratio, and energy attenuation factor. The results show that as the width of the pressure relief zone of the gradient surrounding rock structure increases, the vibration frequency of the stress wave decreases, the amplitude attenuation factor increases, and the energy attenuation factor shows an upward trend, which improves the cushioning and seismic isolation performance of the gradient surrounding rock structure and enhances the burst prevention ability of roadway. When the width of the pressure relief zone is small, the complex superposition of stress waves in the gradient structure will be formed, which makes the amplitude of stress waves surge in the local region. Reasonable width of pressure relief zone can avoid the complex superposition of stress waves in the structure with three media and two planes. The row spacing between boreholes in the pressure relief zone decreases, the elastic modulus and density of the medium in the pressure relief zone of the gradient surrounding rock structure decrease, and the proportion of energy absorption increases, which improves the absorbing performance of the stress wave. The greater the wave impedance matching factor of the three zones in the gradient surrounding rock structure, the greater the energy attenuation factor, that is, the greater the difference in the medium properties of the three zones, the better the attenuation effect of the gradient surrounding rock structure on stress waves. The size and physical and mechanical properties of the pressure relief zone can be changed by adjusting the depth and row spacing of the pressure relief boreholes, which can effectively improve the wave absorption of the gradient surrounding rock structure, cushioning, and seismic isolation performance. Combining with engineering case analysis, it is proved that the surrounding rock with gradient structure can effectively absorb the stress wave energy generated by rock burst and avoid rock burst disasters.
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