Analyze And Distinct Bored Pile Defects Based On Ultrasonic Transmission Method

Pile foundation is a kind foundation which,along with the enlarging of construction,is getting more and more important.Siltedpiles, segregation, honeycomb, centralized air vent and fracture of bored piles often occurs due to geological and hydrological conditions and conducting method, which will have bad influence on pile bearing capacity and safety performances of superstructure.Ultrasonic transmission method is a detecting method, which, compared to other detect method, is light and convenient, efficient, economical, to deduce defects of bored piles by the variation trend of ultrasonic parameters and transmission waves while propagating in concrete. There’re important practical meanings to study signal processing of ultrasonic transmission method for detecting bored piles’ defects while there are still much to do to improve signal analysis accuracy.This thesis mainly done works based on laboratory tests for detecting pile defectsby ultrasonic transmission method, specificallyon bored pilesconsidering its constructing characters, as follows:(1) That ultrasonic transmission method has a broad application potential was drawn by the comparison of the principles and specialties of ultrasonic transmission method with static load testing, core-drilling method, low strain method testing and high strain dynamic testing method.And how pile defects affect ultrasonic sound transmission was analyzed to be as the theoretical basement of signal analysis.(2) A conclusion that wavelet transform is better to deal with saltation processing signal by analyzing signal changes in frequency domain is drawn after analyzing and comparing the way of Discrete Fourier transform, fast Fourier transform, short time Fourier transform and wavelet transform in dealing with ultrasonic signal. So wavelet transform is much more suitable for analyzing non-stationary and periodic signals just as the bored concrete piles’ completeness detecting signal by ultrasonic transmission method.In order to get a proper function to be the basis method of signal analysis in this thesis, different wavelet functions are systematically analyzed and compared, and sym function was chose.(3) To find regular patterns of ultrasonic signal while transforming in defective piles, the transformation characters of four modeling testspecimens with defectsincluding silted pile, segregation, centralized air vent and fracture bored pile were analyzed separately. Analyzing defective piles’ signal by sym function with Matlab software, and the regular patterns are as follows: the specific acoustic impedances of loess and air are much lower than that of concrete. The phenomena of diffraction, reflection and refraction can happen when ultrasonic signal propagating to interfaces between concrete and loess, so the air, which form different beams which interfere and overlap and making ultrasonic parameters sudden change. The sudden changes make wave distortion and make wave velocity and amplitude decrease.(4) Concludes of principle characters and weakness of probabilistic method and Product of Slope and Difference criterion method were found, based on project cases, to show thatauthor’s theories can be useful to distinct defects of bored piles detected by ultrasonic transmission method. This thesis’ methods supplement the lack of probabilistic method and Product of Slope and Difference criterion method, and take both wave velocity and amplitude of ultrasound into consideration, and also frequency-amplitude curve’s changes in frequency domain, while judging bored piles’ completeness through ultrasonic signal which have been proved by project cases.Conclusions are drawn after all above works as follows:(1) The ultrasound velocity is over 4km per second in common and strength well performed piles, while is under 4km per second in piles with defects and whatever the defect is.(2) Wave in normal piles has regular amplitudes and cycle regularity, while defect piles don’t, or values of amplitude differ a lot.Only one main crest appears in normal piles’ spectrum, and main crests’ frequencies are almost the same, while multi-crests and main frequency drifting turn up in defect piles.