Study On The Acoustic Field Distribution And Numerical Simulation Of Acoustic Wave To Detect Pile Integrity With Cross-hole Sonic Logging

With the fast development of city construction in our country, tall buildings,large-scale bridges, marine structures, other large buildings and structures are built continuously. When the shallow stratum of the construction site is not enough to bear the load of the superstructure, pile foundation is widely used. Because of nonstandard construction and bad stability of stratum and other reasons, cast-in-situ pile easily generates defects which affect pile integrity, such as pile bottom sediment, broken pile,shrinking diameter, etc. In order to ensure the safety of buildings and structures and human life, the sizes and positions of defects must be found out. This aim to judges the classification of pile integrity, for engineering treatment. Compared to other testing methods of foundation pile integrity, cross-hole sonic logging has many advantages which contain comprehensive and detailed testing, accurate and reliable results, testing which is not restricted by pile length and pile diameter and stratum around foundation pile, etc.For accurately finding out the sizes and positions of latent defects in pile, this paper improves the testing steps by calculating the sound pressure and the directivity of traffic circle radial transducer in cross-hole sonic logging and getting more laws between acoustic parameters and defects by numerical simulation. Then the testing steps is applied to guide the engineering practice. The main contents are summarized as follows:(1)After systematically analyzing the testing principles of cross-hole sonic logging,the shortcoming of radiated acoustic field of transducer is proposed.(2)Based on the theory of acoustic source radiation, combining with the derivation process of acoustic field of circular transducer, the acoustic pressure and the directivity function of traffic circle radial transducer in the far field in cross-hole sonic logging are calculated. Then the factors of influencing the directivity are analyzed. By means of MATLAB, the directivity function in polar coordinates are drawn. Then the effects of these factors on the directivity are studied.(3)Because the strong directivity represents that the acoustic energy converges around the acoustic testing line, which is not adverse to testing, the strategy of improving directivity and the method of ascertaining the suitable angle in slantwise testing are given.(4)Two-dimensional complete pile concrete model is built. Comparing simulated acoustic velocity with theoretical acoustic velocity shows that the COMSOL Multiphysics software is reliable to simulate the propagation of acoustic wave in concrete. By simulating the propagation of sine acoustic waves of different frequencies in concrete, the law which the directivity intensifies with the increase of frequency is obtained for verifying the theoretical derivation.(5)The various concrete models where the distance between vertical defect boundary and the acoustic testing line gradually changes are built. Comparing the acoustic parameters of these models with those of the complete pile concrete model, the law which are applied to ascertain vertical defect boundary is obtained. The horizontal defect concrete model is built. Comparing the acoustic parameters of the model with those of the complete pile concrete model shows that horizontal defect is found difficulty. Then the method of avoiding losing the judgment of horizontal defect is given.(6)Based on the achievements of the above research work, the testing steps which are improved is applied to guide the engineering practice in which using core drilling method tests the accuracy of testing.