Ultrasonic Response Characteristics Of Red Sandstone With Holes

With the development of social economy and the increasing material needs of the people,the country has gradually increased the mining intensity and depth of mineral resources,and a large number of geotechnical engineering problems have also followed.A large number of studies have shown that there are various macro and micro defects(holes,cracks)inside the rock mass,and the geometric size,shape,distribution and other factors of the defects have a significant impact on the instability and failure of the rock and soil mass.However,limited to the complex underground geological conditions and influencing factors,it is very difficult to identify the cavities inside the rock in situ.In this paper,ultrasonic detection technology is used to study the ultrasonic response characteristics of red sandstone with holes,which provides a basis for in-situ ultrasonic identification of the geometry of the holes and the prediction of failure formation trends,and enriches the theoretical system of instability and damage in rock mass engineering.The original red sandstone in southern Jiangxi was processed into rock specimens with different pore parameters for indoor testing.Through a combination of physical model tests and numerical simulations,the study was conducted from the perspectives of different pore sizes,angles,shapes,numbers and distributions.The ultrasonic response characteristics of the rock with holes inside are analyzed,and the change rule of ultrasonic acoustic parameters with the hole parameters is analyzed.The research results show that:(1)Ultrasonic transducers of different frequencies are used to test the complete rock sample,and the influence of the test frequency on the acoustic parameters is analyzed.It is found that as the test frequency rises,the coupling phenomenon of wave velocity dispersion and energy attenuation occurs.(2)The test analysis of related parameters such as ultrasonic wave speed,amplitude,dominant frequency,attenuation coefficient and other related parameters of red sandstone with holes,found that the wave speed is less sensitive to the holes,while the amplitude,dominant frequency,and attenuation coefficient are more sensitive to the holes.The change trend of amplitude,main frequency and attenuation coefficient difference before and after punching is the same.With the increase of the hole size perpendicular to the direction of ultrasonic propagation,the amplitude of the first ultrasonic wave decreases,the main frequency shifts to the low-frequency end,and the attenuation coefficient increases.(3)COMSOL was used to simulate the propagation process of sound waves in the threedimensional hole model.In the case of a single hole,the hole size has the greatest influence,followed by the hole angle and shape.As the hole size perpendicular to the propagation direction increases,the wave amplitude transmission coefficient It decreases linearly,the main frequency of the transmission boundary drifts slightly to the left,and the amplitude of the Fourier coefficient corresponding to the main frequency gradually decreases.In the case of holes,the number of holes has a greater impact on the propagation of ultrasonic waves.When the number of holes increases,the amplitude transmission coefficient decreases linearly,and the amplitude of the Fourier coefficient corresponding to the dominant frequency gradually decreases.(4)The size of the hole and the angle of the hole are proportional to the peak size of the maximum sound pressure,and the degree of discretization of the hole distribution is inversely proportional to the peak size of the maximum sound pressure.The size of the hole parallel to the propagation direction is proportional to the sound pressure extreme.The time point at which the large peak occurs is positively correlated,and the number of maximum sound pressure peaks is related to the number of holes.A comprehensive analysis of the number,size and location of the peaks can qualitatively determine the relationship between the geometric shapes of the holes.