Study On Simulation Of Pile Foundation Detection Based On Acoustic Transmission And Acoustic Wave CT

With the rapid growth of construction projects in China,large diameter and super-long pile foundation has been widely used in urban construction and bridge engineering.The quality of pile foundation affects the safety and reliability of buildings and bridges directly.Therefore,pile foundation detection has important practical significance.The acoustic transmission is a method to determine the quality of the concrete on the acoustic propagation path by using the acoustic energy attenuation,velocity and dominant frequency changes as well as waveform distortion.The acoustic transmission method has the advantages of high efficiency,reliable results and no limitation of pile length and has become an important means for the pile foundation integrity detection.In this paper,the finite element method was used to simulate the propagation process of acoustic waves in the pile foundation.The various acoustic parameters were analyzed in the time domain and frequency domain.The propagation law of the acoustic wave in the defective concrete pile foundation was studied.The acoustic tomography technique was applied to the large diameter pile foundation detection,and the internal quality of the pile foundation was retrieved by using the acoustic information,which provides a reliable basis for the detection of pile foundation defects by using acoustic tomography.The main contents and conclusions are as follows:(1)The basic principle and signal analysis method of pile foundation acoustical transmission technology are introduced.The theoretical basis,imaging idea and imaging inversion algorithm of acoustic tomography which used in the pile foundation detection are summarized.These studies provide the theoretical basis for finite element simulation research.(2)The propagation process of acoustic wave in large diameter pile foundation was simulated by using finite element software ANSYS / LS-DYNA,which avoids the influence of poor sensor coupling and noise interference during the experiment of pile foundation acoustic wave detection.The calculation accuracy of the pile foundation wave problems which use finite element method was verified by the calculation of wave velocity.The characteristics of acoustic wave propagation in the defective connect with the change of the linear dimension of the defects were analyzed.The received signals of different defect types were analyzed in time domain and frequency domain respectively,and the frequency pedigree distortion coefficient was studied.The influence law of vertical linear dimension and horizontal linear dimension of the defects,hole size and material parameters on received acoustic signals in time domain and frequency domain were discussed.The results showed that the acoustic wave energy concentration was suitable for analysis of the large diameter pile detection signal.The vertical linear dimension of the defects,hole's size and material parameters had significant influence on the wave velocity,amplitude and main frequency,but the horizontal linear dimension of the defect had relatively small effect on the wave velocity,amplitude and main frequency.The frequency pedigree distortion coefficient was sensitive to the acoustic energy attenuation.The difference of the frequency pedigree distortion coefficient among different defect types was significantly.(3)The detection steps of acoustic tomography was introduced,which against the particularity and complexity of pile foundation detection.The finite element software was used to simulate the propagation process of acoustic waves in different diameter and different detect size of pile foundation,and the initial wave travel time was taken as the inversion parameter to inverse the pile imaging.The results of acoustic tomography with frequencies of 50 kHz and 100 kHz were compared.The results of acoustic tomography were compared with the flat and oblique observation systems.The results showed that the acoustic wave with 50 kHz frequency was suitable for acoustic tomography imaging of large diameter pile foundation.However,the acoustic wave with 100 kHz frequency was suitable for acoustic tomography imaging of pile foundation whose diameter less than 1 meter.The flat measuring observing system for acoustic CT imaging was better,when the horizontal dimension of the rectangular defect was within 0.4 meter.However,when the horizontal dimension of the defect was greater than 0.4 meter,the acoustic CT imaging should be carried out by the oblique observation system.