Experimental Study On The Spectrum And Band Energy Characteristics Of Rock Stress Waves With Gradient Static Stress

Gradient stresses in rocks are widely found in underground rock masses and engineering rock enclosures,and the gradient stress environment with changing spatial locations induces different deformations of rocks and affects the physical and mechanical properties of overall rocks,which in turn leads to complex propagation and attenuation characteristics of stress waves in rock masses with gradient stresses.In order to solve the problem of obtaining the best blasting effect and maintaining the stable environment of engineering rock in blasting construction,experimental research on the deformation characteristics and dispersion characteristics of stress wave propagation in rocks subjected to different gradient static stresses is carried out.The main research contents and conclusions of this paper are as follows:(1)In order to study the effects of different gradient stresses on the deformation characteristics of the rocks,Linear and nonlinear gradient stresses were applied to the yellow sandstone specimens with large porosity using the existing gradient stress loading test device in the laboratory.The results show that the axial strain of the rock under the gradient stress is at different stages of uniaxial compression deformation at different spatial locations;the axial strain of the rock under the gradient stress increases nonlinearly with the increase of spatial distance,and the initial axial strain of the rock changes faster with the distance of the measurement point as the stress gradient increases,and the axial strain of the rock changes abruptly with the increase of the distance of the measurement point when the maximum stress gradient is set.The axial strain of the rock changes abruptly with the increase of the measurement point distance when the maximum stress gradient is set;the axial strain of the rock at different measurement point positions corresponds to different stages of its uniaxial compressive deformation.(2)Based on the time domain data of stress wave propagation in rocks under different gradients of stress,the changes of stress wave spectrum amplitude,center-of-mass frequency and spectrum peak with stress wave propagation distance and stress gradient are studied to characterize the dispersion characteristics of stress wave propagation.The results show that the amplitude of the stress wave spectrum is mainly distributed in the range of 0～10 k Hz,with the increase of frequency,the spectrum amplitude shows a trend of increasing and then decreasing,and a single peak is formed near 1 k Hz,indicating that the main frequency of the shock stress wave signal is around 1 k Hz;under the same stress gradient,with the increase of the propagation distance,the stress wave center-of-mass frequency shows an " Under the same stress gradient,with the increase of propagation distance,the stress wave center-of-mass frequency shows an "increasing-smooth-decreasing" trend;the spectrum peak decreases rapidly and then develops smoothly with the increase of propagation distance;before the axial strain of the rock reaches the strain of uniaxial compressional failure damage stage,the stress wave center-of-mass frequency and the spectrum peak appear anomalous.(3)Based on the time domain data of stress wave propagation in rocks with different gradient stresses,the decay characteristics of the total energy of stress waves and the distribution of frequency band energy are studied by wavelet packet decomposition and reconstruction.The results show that the total energy of stress waves in rocks without gradient stress decays linearly;the decay of the total energy of stress waves in rocks with gradient stress shows the trend of "rapid decrease and then smooth development",and decays exponentially;in the frequency band energy,the energy component of stress wave signal is mainly low frequency,and the energy proportion of high frequency is very small.The low frequency band0 ～ 31.25 k Hz accounts for 80% ～ 95% of the energy.The energy distribution of stress wave frequency band with the propagation distance also has the phenomenon of spectral shift,which is consistent with the conclusion of the center of mass frequency;with the change of nonlinear stress gradient,the energy distribution of stress wave frequency band through measurement point 6 in the rock also has a significant difference,and the percentage of energy corresponding to each level of frequency band is different,which affects the attenuation and dispersion characteristics of stress wave.The energy share of each frequency band is different,which affects the attenuation and dispersion characteristics of stress waves.