Experimental Study On The Influence Of Confining Pressure And Water Content On Stress Wave Propagation In Red Sandstone

The blasting excavation of deep rock mass engineering has a damage effect on the buildings or structures in the middle and far areas of the explosion source,and its effect is related to the size of the blasting dynamic load and the propagation attenuation from the explosion source to the buildings or structures.Therefore,it is of great theoretical and practical significance to study the influence of confining pressure on the propagation and attenuation of rock stress wave for the safety and stability evaluation of adjacent buildings or structures during blasting excavation of deep rock mass.The confining pressure and water content have a great influence on the static physical and mechanical properties of rock.With the increase of confining pressure,the density,elastic modulus and static strength of rock gradually increase,while the water content has a weakening effect on the mechanical properties of rock,which will affect the attenuation performance of rock stress wave propagation.The main research contents and conclusions of this paper are as follows :(1)The influence of confining pressure on rock acoustic wave propagation characteristics can characterize the change of rock wave impedance,which can lay a foundation for studying the propagation characteristics of rock stress wave.In order to explore the influence of confining pressure and water content on rock acoustic wave propagation,single and cyclic confining pressure loading were carried out on red sandstone specimens with different water contents,and the acoustic wave velocity was measured in real time to study the variation of acoustic wave velocity and wave impedance of red sandstone with confining pressure.The results show that in the process of single confining pressure loading,the increase of confining pressure is beneficial to the propagation of acoustic wave in red sandstone.With the increase of confining pressure,the acoustic wave velocity of red sandstone increases step by step,and the acoustic wave velocity of saturated rock shows a trend of ’ steady development,linear increase,stable unchanged,sharp decrease ’.In the process of cyclic loading and unloading,the acoustic wave velocity of red sandstone decreases with the increase of loading times,and the reduction of acoustic wave velocity increases gradually.(2)Based on the improved Hobkinson pressure bar,the stress wave propagation tests of red sandstone specimens under different confining pressure conditions were carried out.The effects of confining pressure and water content on the stress wave waveform,transmittance,reflectivity and stress wave propagation velocity of red sandstone were analyzed.The results show that with the increase of confining pressure,the amplitude of transmitted wave increases gradually,and the amplitude of reflected wave decreases gradually.The multiple transmission and reflection of stress wave is the main factor leading to the occurrence of compression wave at the tail of reflected wave.The confining pressure is beneficial to the stress wave propagation of rock.The transmittance and propagation velocity of stress wave increase with the increase of confining pressure,and the reflectivity decreases with the increase of confining pressure.(3)Based on the time domain data of stress wave propagation in red sandstone under different confining pressures and dynamic loads,the frequency spectrum,peak frequency,dominant frequency and centroid frequency of stress wave are obtained by fast Fourier transform to characterize the dispersion characteristics of stress wave propagation.The results show that the confining pressure and water content do not change the spectrum of the incident wave,but the increase of confining pressure has a significant effect on the spectrum of the incident wave and the reflected wave.With the increase of confining pressure,the amplitude of the reflected wave decreases gradually,and the opening of the spectrum curve becomes larger and larger.The amplitude of the transmitted wave gradually increases,and the opening of the spectrum curve becomes smaller and smaller.In the natural state of red sandstone,the spectral peak,main frequency and centroid frequency of the reflected wave gradually decrease with the increase of confining pressure.The spectral peak,dominant frequency and centroid frequency of the transmitted wave gradually increase with the increase of confining pressure.In the saturated state of red sandstone,the spectral peak of the reflected wave gradually decreases with the increase of confining pressure,and the main frequency and the centroid frequency gradually increase with the increase of confining pressure.The spectral peak of the transmitted wave increases with the increase of confining pressure,and the dominant frequency and centroid frequency decrease with the increase of confining pressure.