Research On Pulse Echo Dynamic Pile Testing

Pulse Echo dynamic pile testing method is the most often used pile integrity test methods. Base on the one-dimensional stress-wave theory, the test data can be interpreted by intuitive method in time-domain or frequency-domain. Because of the qualitative analysis the precision and the reliability usually can't satisfy the engineering demand.In order to resolve the problem in pile integrity testing, the characteristic of wave propagating along the pile-soil system and the test signal interpret methods have been studied systematically.(1) Performed the model pile testing and the soil samples dynamic testing. Soil dynamic properties index about the test site were acquired, pulse echo dynamic test figures of model piles enclosed with soil and without soil were also acquired and analysed systematically.(2) By means of finite element method, the relationship of wave speed and wave amplitude decay to soil behaviour were researched.(3) The wavelets analysis method was introduced into the field of pile integrity testing, the wavelet theory was also introduced and some applications of the wavelet analysis to pile testing were attempted,such as denoise methods, the ways of separating soil resistanced wave from the test curve and the interpreting means of testing figure for shallow defected piles.Base on the above works, some positive results were acquired as follow:(1) Because of the size effect, the traveling speed of pulse wave along the pile is no longer a constant value. With the increasing of propagating distance, the wave speed may be larger, equal, or slower than the one-dimensional rod wave speed.(2) The static resistance from soil around pile can increase the wave travel speed, but the damping can decrease the wave speed, the final results depend on the superposition of both effects and usually it makes the wave speed slower.(3) traveling speed of wave along the pile is also affected by the state of stress, the wavespeed between upward and downward is different, wavespeed of upward tensile wave is swifter than the downward speed, the wavespeed of upward compression wave is slower than the downward wavespeed.(4) Wave amplitude decay in different ways by downward compressive wave and upward wave, the upward wave decay slower than the downward wave. Downward wave amplitude decay in negative exponential function, but the upward wave amplitude is not the case. In practice, engineers and technicians always magnify the test data according to the exponent rule to decreasing the effect of soil.(5) To make use of wavelet analysis, the test signal can be decomposed on wave band, so the complex signal become several simply signals, so we can treat it in an easy way.(6) Some analysis on test data for the pile enclosed by soil show that different wave bands travel in similar speed, but the amplitude decay severe with the frequency increasing.