Influence Of Three-dimensional Static Stress On Stress Wave Propagation Characteristics In Red Sandstone

The engineering rock masses are subjected to three-dimensional in-situ stress,and the static stress can change the microstructure inside the rock,and then change the propagation attenuation characteristics of the stress wave in the rock.In this paper,the modified Split Hopkinson Pressure Bar is used to test the stress wave propagation of red sandstone.Based on different loading modes,the influence of three-dimensional static stress on the stress wave propagation of rock is qualitatively analyzed,and the theoretical analysis and test results are mutually verified.The main research contents and results of this paper are as follows:(1)The stress wave propagation velocity of input bar and output bar is measured by verification test.By comparing the incident wave and the transmitted wave,it was found that the stress wave shape of them was consistent and the amplitude was equal,which verified the effectiveness of the test method.(2)Under the same confining pressure,with the increase of axial pressure,the stress wave velocity of red sandstone first increases rapidly,then develops gently,and finally decreases rapidly.The transmission coefficient increases gradually,then develops gently,and then decreases.The absolute value of the reflection coefficient decreases sharply and then increases slightly.The higher the confining pressure grade is,the greater the peak value of the rock stress wave velocity and transmission coefficient is,and the smaller the minimum value of the absolute value of the reflection coefficient is.(3)With the increase of confining pressure,the stress wave velocity of rock increases gradually.The transmission coefficient increases gradually,but the increase rate decreases.The absolute value of reflection coefficient decreases gradually and the rate of decrease is slow.The transmission coefficient first increases and then decreases under low confining pressure effect,and then increases under high confining pressure effect.The change of absolute value of reflection coefficient is opposite to that of transmission coefficient.The stress wave velocity is positively correlated with the confining pressure,and the permeability and reflection coefficient have a good quadratic function relationship with the confining pressure.(4)Based on the empirical relationship between the stress wave velocity and the static stress obtained by the test and the empirical model of the longitudinal wave velocity and density,the relationship between the wave impedance and the static stress is obtained: as the axial pressure increases,the wave impedance first increases and then decreases,and the higher the confining pressure level is,the larger the peak value of the wave impedance is.Under the condition of different axial pressure,the wave impedance increases with the increase of confining pressure.When the confining pressure is small,with the increase of axial pressure grade,the wave impedance at the same confining pressure increases first and then decreases.When the confining pressure is large,with the increase of the axial pressure grade,the wave impedance under the same confining pressure increases.(5)According to the theory of one-dimensional stress wave was deduced through trend along with the change of wave impedance and reflection coefficient contact wave impedance and the relationship between the static stress,the transmission coefficient under different working condition of static stress of the theoretical,and compared with the corresponding experimental values,the percentage difference within 10%,validate the correctness of the theoretical analysis results.The research results of this paper can not only provide new ideas for the measurement of physical parameters of deep rock mass,but also serve as a theoretical reference for the stability analysis of engineering surrounding rock mass,which is of great significance for ensuring the safe and efficient construction of deep engineering rock mass excavation.