Pile length estimation based on guided wave theory and dispersion analysis for reuse of foundations

Abstract

The construction of new structures on existing pile foundations can significantly reduce the overall project costs. The reuse of foundations requires information on the embedded depth of existing piles, which is not always known. In this paper, a novel technique based on the periodic analysis of the phase difference and the 3-dimensional guided wave theory was developed to effectively estimate the embedded depth of unknown foundations. In this method, the guided wave model of a cylindrical pile is built by the spectral element method to determine the dispersion relation. A modified Ridders’ algorithm is proposed for root-searching. According to the phase difference of the responses collected by at least two sensors located on top or the lateral side of the pile, and the dispersion relation obtained by the spectral element method, the dispersion analysis diagram can be obtained to show the relationship between the phase difference and the wavenumber. Through the periodic properties of the dispersion analysis diagram, the pile length can be estimated. Furthermore, the periodic analysis of the phase difference for the signals collected on top of the pile is conducted in this paper using the 3-dimensional guided wave model-based dispersion relation. By comparing with synthetic and experimental data, it was shown that the proposed method can achieve an accuracy of greater than 95% in estimating the pile length of unknown foundations.