Integrity Testing Of Piles Based On Finite Element Methods And Wavelet Transformations

Low strain integrity testing of piles has been recognized and accepted in the last few decades for its simple theory, easy operation and cheap equipment. In the engineering field it is now used cosmically. Even though there are still many mistakes in the low strain integrity testing of piles. Further more in some conditions this theory is inapplicable at all. There are two primary causes: The theory of reflected wave is so simple that the formula of the theory has multi-solution sometimes just because there are too little parameters in the formula. Therefore under some certain conditions this theory is inapplicable because we are not able to choose an accurate one in those solutions without any other referrence. Now the datum collected from the pile cap are usually analyzed in time domain, or simply in time and frequency domain both. But this is insufficient for getting enough information for judgement. That is to say sometimes the results are not so accurate because we have not fully take advantage of these datum. In this paper the common methods used in the integrity testing of piles were summarized and analyzed. And then two complicated models were studied in detail by using FEM and wavelet transformation. What have been studied in this paper are listed below: 1. The models were built in FE program ABAQUS, and then the frequency authenticity and stability of the FE results were studied by means of comparing the frequency component of the same model partitioned into different numbers of finite element, comparing the dispersion character of FE result with the theory formula and comparing the reflected wave of isolation layer in time domain with what it is in real piles. In doing so it was proved feasible for using the FE result as the datum source of low strain integrity testing of piles, which are to be analyzed with wavelet. 2. First the excellent ability of wavelet transformation in time-frequency analysis was introduced, Secondly taking into account the character of the paper, the principle of choosing wavelet was made certain and wavelet SYM2 was select to be used in this paper. In the end the continue wavelet coefficients were select to be the standard in analyzing the result. 3. When the reflected waves of the diameter-extended piles and the integrated piles with a hard soil layer surrounded were contrasted, it is proved as what could be deduced from the theory of reflected wave that their figures have no obverous difference in time domain. Then wavelet transformation was applied in analyzing these two models, and some different characters were found. The Huygens theory and the dispersion theory of waves are applied to explain the characters in these two models'wavelet transformation results. At last a group of crests in high frequency between the reflected wave of bug and the pile toe were provided to be the distinguishing character between the diameter extended piles and the piles with a hard soil layer surrounded.