Study On Stress Wave Dispersion And Energy Characteristics Of Red Sandstone By Three-Dimensional Static Load

The rock mass has different stress distribution due to the different depths.As the depth of the burial increases,the ‘three high' characteristics of the rock mass become more obvious.At present,owing to the efforts of many scholars,the dynamic mechanical properties of rock mass under three-dimensional static loading have achieved fruitful results,but the stress wave propagation law in rock mass under three-dimensional static loading has been rarely studied.Therefore,it is of great theoretical value to consider the attenuation characteristics of stress wave propagation in rocks under three-dimensional static loading.In this paper,the red sandstone of Ganzhou was selected as the research object.Based on the modified split Hopkinson pressure bar with coupling static and dynamic loading,the stress wave propagation experiments under different three-dimensional static stress conditions were carried out on the red sandstone specimens,and the frequency spectrum,the dominant frequency and the energy evolution were discussed.The main conclusions are as follows:(1)The frequency spectrum of the incident wave and the reflected wave are parabolic in all static stress conditions.That is,as the frequency increases,the amplitude of the corresponding-frequency wave increases first and then decreases to zero.The transmit wave spectrums also change with the variation of the static loading,and all of them change from parabolic to hyperbolic.Compared with that under the condition of fixed axial pressure-variable confining pressure,the variation magnitude of frequency spectrum is more remarkable under the condition of fixed confining pressure-variable axial pressure.Meanwhile,it is seen that under different static stress conditions,the distribution of the preponderant frequency almost keeps constant varying from 0 to 3 kHz.(2)Due to different setup of the static load under the two loading conditions,which leads to different deformation of internal pores in the rock,the variation laws of dominant frequency are also different.Under the condition of fixed confining pressure-variable axial pressure,as the axial pressure increases,the dominant frequency of incident wave and transmit wave increases first and then decreases,while the variation of the dominant frequency of reflected wave is contrary.Under the condition of fixed axial pressure-variable confining pressure,as the confining pressure increases,the dominant frequency of the incident wave does not change significantly,and the dominant frequency of the transmit wave gradually increases.(3)Under a given confining pressure,the transmission factors for energy increase firstly with the increase in the axial pressure.While the axial pressure is increased to 60%-80% of the corresponding 3D compressive strength,the transmission factors for energy tends to decrease.Under a given axial pressure,with the confining pressure increasing,the transmission factors for energy increase continuously.Furthermore,under the axial pressure lower than the 60% of the 3D compressive strength,the dissipative energy of rock specimens increase with a decreasing rate;while the axial pressure is higher than the 60%-80% of the 3D compressive strength,the dissipative energy of rock specimens tends to decrease.(4)Regardless of the static load conditions,the length-to-diameter ratio of the test piece has an effect on the dominant frequency and energy variation of the transmitted wave during stress wave propagation.The main performance is as follows: as the aspect ratio increases,the main frequency of the transmitted wave decreases gradually,and the transmission energy of the rock specimen decreases gradually,while the dissipative energy shows an "increasing-stable constant-decreasing" trend.