Nondestructive Method for Length Estimation of Pile Foundations Through Effective Dispersion Analysis of Reflections

Abstract

Motivated by the important problem of unknown foundations, a nondestructive evaluation technique, named effective dispersion analysis of reflections (EDAR), is developed for estimating embedded depth of pile foundations. EDAR testing involves laterally exciting the pile with the hammer and measuring the accelerations at two other points on the pile. The novelty of EDAR comes from the processing these signals; unlike existing methods, EDAR accurately captures the effect of physical dispersion of the waves as they propagate in the pile, and the reflections from the pile tip. The key to data processing is the EDAR plot, which is a plot of phase difference between the two responses as a function of newly introduced effective wavenumber that encapsulates the wave dispersion characteristics. The methodology is easy to use in that a simple formula can convert the oscillatory characteristics of EDAR plot to the unknown embedded depth. This paper contains the derivation of the underlying formulation followed by verification with synthetic models and validation in laboratory settings, resulting in less than 5% error in embedded length.