Research On The Influence Of Static Stress On The Rock Stress Wave Waveform

Underground rock masses are often subjected to in-situ stress.Understanding and mastering the variation mechanism of rock stress wave waveform under in-situ stress is helpful to explore the mechanism of stress wave propagation and attenuation.In order to study the influence of three-dimensional in-situ stress on rock stress wave,this paper abstracts the in-situ stress as three-dimensional static stress,and conducts stress wave propagation experiments under one-dimensional static stress and three-dimensional static stress respectively.According to the characteristics of the influence of static stress on the rock stress wave shape,the rising edge,falling edge,wave section and wave tail strain variation section are analyzed.Meanwhile,the centroid frequency,frequency band energy,box dimension and correlation dimension are used to study the dispersion characteristics and fractal characteristics of the stress wave shape variation mechanism.The main research contents and conclusions are as follows:(a)The stress wave propagation experiments of long rock specimen under onedimensional static stress is carried out by means of dynamic and static loading device.According to the characteristics of rock stress wave under one-dimensional static stress,the wave shape is divided into rising edge,falling edge and fluctuating section,and the variation mechanism of waveform are studied,and the centroid frequency,frequency band energy,improved box dimension and correlation dimension are used to study the variation mechanism of waveform.The results show that the axial static stress changes the stress waveform,causing it to exhibit fluctuating and elevating sections.Propagation distance does not change the shape of the waveform but decreases the slopes of the rising,falling,and fluctuation sections.The centroid frequency trend of the stress wave can reflect the complexity of the rock stress wave waveform.Variation in the stress waveform slopes(rising edge,falling edge,and fluctuation section)is consistent with that of the centroid frequency.The low-frequency energy(2197–3661 Hz)migrates in the high-frequency direction to change the stress waveform;the energy transfer direction of the overall frequency band of the stress waveform in the range 0-4 k Hz(rising edge,falling edge,and fluctuation section)can reflect the variation in its centroid frequency.The rectangular grid and the stress wave box dimension model of the same space background can reflect the fractal characteristics of the rock stress wave under different static axial stress.With the increase of the axial static stress,due to the increase in the complexity of the stress wave waveform,the box dimension of stress wave increases.The correlation dimension of the stress wave cannot reflect the similarity of the waveform,but can only reflect the density of the point set at the smallest scale.As the axial static stress increases,the correlation dimension of stress wave is oscillating all the time without obvious changing trend.(b)The stress wave propagation experiments of rock specimen under three-dimensional static stress is carried out by means of dynamic and static loading device.According to the characteristics of the stress waveform,the variations of the stress wave wavelength,the rising edge,the falling edge and the strain of the wave tail are analyzed,and the stress wave dispersion and fractal characteristics of the rock under three-dimensional static stress are analyzed.The results show that axial static stress has great influence on the stress wave shape characteristics,while confining stress has little effect on the waveform.With the increase of axial static stress,the wavelength of reflected wave increases,the strain of waveform tail decreases first and then increases,and the slope of rising and falling edges decreases.Both the length and the strain value of the transmitted wave tail increase,while the slope of the rising and falling edges decrease.The variation trend of centroid frequency of stress wave is determined by the change of energy proportion in each frequency band within 0-12 k Hz in the bandwidth.The increase of energy proportion in the frequency band between 4-6k Hz leads to the overall increase of centroid frequency of transmitted wave.The increase of the energy proportion in the frequency band 0-6k Hz leads to the decrease of the centroid frequency of the reflected wave.The improved three-dimensional stress wave box dimension model under static stress can reflect the variation of waveform.With the increase of axial compression,the box dimension of reflected wave increases,and the box dimension of transmitted wave oscillates.