Research Of Ultrasonic Propagation Characteristics In Sandy Silty Clay Under Different Temperatures

The artificial freezing method is a special technique in underground construction.In the process of tunneling construction,forming a certain strength and thickness of freezing wall is the key to ensure the safe and smooth.Once the artificial freezing wall fails,it will lead to unpredictable consequences.Therefore,it is very important to effectively judge the development of freezing wall.At present,the commonly used methods to judge the development of freezing wall are temperature data speculation method,hydrological hole water level observation method,freezer longitudinal temperature determination method and ground penetrating radar detection method.Under normal circumstances,the above methods can effectively judge the development of frozen wall.However,in the face of complex and changeable geological conditions and construction conditions,there is also a situation that can not accurately grasp the development status of freezing wall through the above means.Therefore,it is urgent to explore a new detection method for the development status of freezing wall.Ultrasound non-destructive testing technology is an efficient,convenient,accurate and adaptable detection method.It has a considerable number of applications in geotechnical engineering.Relevant research shows that before and after the freezing of soil,the acoustic parameters will vary with the change of phase state and the decrease of temperature.Therefore,the ultrasonic testing technology can be used as a means to detect the development of freezing wall.However,the theory of detecting the development of frozen wall by ultrasonic wave is still very deficient,and the simulation study of ultrasonic wave propagation in frozen stratum is relatively scarce.In this paper,through theoretical analysis,laboratory tests and numerical simulation,the ultrasonic propagation characteristics of sandy silty clay under different freezing temperatures are systematically studied.The specific research contents and results are as follows:The acoustic parameters of artificial frozen soil under different conditions are obtained by using orthogonal test with three levels of temperature,water content and density,and temperature single factor test with constant water content and density.The variation law of acoustic signals is analyzed,and the temperature,ultrasonic wave velocity and attenuation coefficient under different conditions are established.Relational expressions.Sensitivity analysis shows that ultrasonic wave velocity is sensitive to temperature and water content,but less sensitive to density.Attenuation coefficient is sensitive to temperature,less sensitive to water content and less sensitive to density.The research thinking of the coupling of temperature field and acoustic field of frozen wall is put forward,and the way of one-way and indirect coupling of sound and heat is determined.Using the finite element software COMSOL,the acoustic transient module of solid heat transfer and pressure is selected,and the simulation model of one-way and indirect coupling of sound and heat is established.The ultrasonic response characteristics of sandy silty clay layer in different freezing stages are obtained.The results show that the frozen wall has never been used before.The peak sound pressure of frozen 42d(intersection)is 45.91% higher than that of frozen 40d(non-intersection).Therefore,the intersection of frozen wall can be judged effectively.The results of laboratory test and numerical simulation of acoustic-thermal coupling in artificial frozen soil can provide reference and data support for the research of ultrasonic propagation characteristics and the development of detection technology in artificial frozen wall of sand-silty clay layer,and have strong theoretical value.