Stress Wave Propagation Attenuation Characteristics Of Red Sandstone Under Gradient Static Stress

Due to the unloading of rock mass in the deep after excavation,the surrounding rock mass is in a gradient geostress environment.In order to study the propagation attenuation characteristics of blasting stress waves in surrounding rock masses under gradient in-situ stress,based on the self-developed test system for stress wave propagation of rock with gradient stress,the deformation characteristics and stress wave propagation characteristics of red sandstone under gradient stress conditions were developed.According to the experimental research,the mechanism of stress wave propagation attenuation was analyzed based on the deformation characteristics of red sandstone under gradient stress.The main research contents and conclusions of this article are as follows:(1)The gradient stress loading test device was used to apply linear and nonlinear gradient stresses to the red sandstone,and the effects of different gradient stresses on the deformation characteristics of the red sandstone were studied.The results show that under the effect of linear gradient stress,the axial strain of red sandstone increases nonlinearly with the increase of space distance,and with the increase of linear gradient stress,the curvature of the strain-space distance curve becomes smaller and smaller.Under the action of nonlinear gradient stress,the strain value increases in a nonlinear form with the increase of the spatial distance.As the nonlinear gradient stress increases,the curvature of the axial strain curve becomes larger and larger.(2)Based on the stress wave propagation test data of red sandstones with different gradient stresses,the stress wave propagation attenuation characteristics are characterized by studying the changes of stress wave width,platform strain,and amplitude.The results show,the gradient stress has a significant effect on the wave profile of stress wave,which is mainly manifested in three aspects:wave width,platform strain,and amplitude attenuation.At the same measurement point,the wave width gradually decreases with the increase of the stress gradient,and the decrement also decreases with the increase of the stress wave propagation distance.Affected by the gradient stress,a platform is formed at the tail of the unloading phase of stress wave,and strain values at the platform have a linear attenuation characteristic with the increase of the propagation distance,moreover,the attenuation rate gradually increases with the stress gradient increasing.The amplitude of the stress wave decays exponentially in space and time.The spatial attenuation coefficient?_x first increases and then decreases with the increase of stress gradient k.The temporal attenuation coefficient?_t also has a similar change law.The spatial amplitude intensity?_x decreases approximately exponentially with increasing stress gradient k,while the temporal response intensity?_t increases first and then decreases with increasing stress gradient k.(3)Based on the stress wave propagation test data of red sandstones with different gradient stresses,the frequency characteristics of stress waves and the law of energy change are studied.The results show,when the gradient stress is constant,the spectrums of signals obtained by each measurement point are parabolic.Within lower frequency range,the variation of spectrum are remarkable with increasing frequency,and within higher frequency range,the spectrum tends to stabilize.At the same measurement point,the dominant frequency of stress wave gradually increases with the increase of the stress gradient;at different measurement points,the dominant frequency decreases with the increase of propagation distance without gradient stress;under a gradient stress,the dominant frequency increases with propagation distance.The total energy of the stress wave dissipates exponentially with the propagation distance,and the energy dissipation coefficient u_x increases first and then decreases as the stress gradient increases.The energy of the stress wave is mainly concentrated in the frequency band of 0 to 36.62 kHz.The energy of the low frequency signal is more sensitive to the expression of gradient stress and propagation distance.