Study And Application Of Ultrasonic Propagation Characteristics In Red Sandstone Saturation Process

Rock softening in water will affect the stability of surrounding rock and even threaten the safety of construction,which is a difficult problem in geotechnical engineering design and construction.Rock has both mechanical and acoustic characteristics,and there is an internal relationship between acoustic characteristics and mechanical characteristics,so we can study the mechanical characteristics of rock through acoustic characteristics.Therefore,it is of great theoretical significance and engineering value to study the ultrasonic propagation characteristics of rock during water absorption and softening.In this paper,taking red sandstone as the research object,aiming at the research and application of ultrasonic wave propagation characteristics in the process of red sandstone saturation,the experiments of longitudinal and transverse wave propagation,numerical simulation of ultrasonic wave propagation and uniaxial compression experiments under saturated conditions were carried out,and the changing law of ultrasonic wave propagation characteristics in the process of red sandstone saturation was explored,focusing on the sensitivity of acoustic parameters to rock saturation,uniaxial compressive strength and elastic modulus.The uniaxial saturated compressive strength of red sandstone was established based on the duration of longitudinal wave core waveform and amplitude attenuation coefficient of transverse wave in time domain,respectively.The main conclusions are as follows:(1)Under the condition of longitudinal wave,the dominant frequency of red sandstone decreases with the increase of saturation;The amplitude of dominant frequency has a linear negative correlation with the increase of saturation.The core waveform duration(the duration from the first take-off peak of the first complete band of the real-time domain signal to the previous peak of the tail band)is defined.The core waveform duration of P-wave has the best characterization of the saturation degree of red sandstone,and the correlation coefficient is 0.91,showing a negative correlation.Under the condition of shear wave,the change of time domain waveform can qualitatively judge the water absorption degree of red sandstone.The attenuation coefficient of amplitude in time domain increases with the increase of saturation degree of red sandstone,and its characterization performance is good,and its correlation coefficient is 0.89.(2)Through the ultrasonic numerical simulation analysis,under the condition of longitudinal wave simulation,the established numerical model can better characterize the timedomain core waveform duration change of sandstone during water saturation,and the deviation rate of the verification sample is between 0.56% and 9.77%;Under the condition of shear wave simulation,the established numerical model can represent the change of time domain attenuation coefficient of sandstone during water saturation,and the deviation rate of the verified samples is between 0.63% and 11.3%.The model can provide a reference for the study of acoustic characteristics of sandstone during softening.(3)The duration of the core waveform of P-wave increases logarithmically with the increase of the elastic modulus of saturated red sandstone,and linearly with the increase of uniaxial saturated compressive strength of red sandstone.The regression equation established by the core waveform of P-wave in time domain has the best characterization performance for the elastic modulus of saturated red sandstone,and its deviation rate is between 1.15% and4.93%.The attenuation coefficient of shear wave amplitude in time domain decreases with the increase of elastic modulus of saturated red sandstone,and decreases with the increase of uniaxial saturated compressive strength of red sandstone.The regression equation established by the attenuation coefficient of shear wave amplitude in time domain is better,and its deviation rate is between 0.78% and 9.13%.