Apparent wave velocity inverse analysis method and its application in dynamic pile testing

This study proposes a new non-destructive testing method (NDT), namely the apparent wave velocity of piles (AWVP) inverse analysis method, to solve the detection problem of the gradually varying cross-sectional defects (cracks or necking) and the material property defects (concrete disintegration or steel corrosion) of piles. The analytical solution of the AWVP has been derived based on the additional mass model. The rationality and accuracy of the theoretical model have been validated through the comparisons with the experiment results. The variation mechanism of the AWVP due to the presence of soil has been clarified. A parametric study is conducted to investigate the major factors to determine the variation tendency of the AWVP. The optimum working conditions and parameter combinations of the AWVP based NDT method have been recommend. The main conclusions can be drawn as: (1) the variation of the AWVP with respect to frequency can be generally divided into a sensitive zone and a stable zone. (2) The AWVP initially decreases rapidly with the frequency within the sensitive zone, however when the frequency decreases to the stable zone, this decline tendency becomes much smaller. (3) Although the AWVP varies extensively within the frequency sensitive zone, this frequency range can substantially relax the requirements for the parametric accuracy of the pile-soil system.