Determining Length of Pile Foundations by Analyzing Response to Lateral Hammer Impact-Paper

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The paper presents Effective Dispersion Analysis of Reflections (EDAR), a nondestructive method for estimating the length of pile foundations from responses to lateral hammer impacts. Unlike conventional approaches that rely on subjective peak-picking in time-domain signals, EDAR analyzes the frequency-dependent phase difference between accelerometers mounted at different positions on the pile. By expressing the response using an effective wavenumber based on the relevant wave-dispersion model, the method identifies characteristic oscillations associated with sensor spacing and reflections from the pile tip. Their period ratio can be used to estimate distance to the boundary without initially knowing wave velocity.<br /><br />The method was tested on concrete-filled steel tubes in laboratory and field settings. Laboratory estimates were consistently within approximately 5% of the known length. In field tests, surrounding soil caused waves to attenuate differently, making reflected signals dominated by secondary longitudinal waves and leading to substantial underestimation with the original analysis. A modified procedure accounts for this effect by using the initial-wave cycle period to estimate material properties and wave velocity, then combining that velocity with the reflection-related wiggle period to estimate pile length. This improved the average field estimate to within 6.3% of the documented length; overall, the authors report estimates within 10%.<br /><br />The results indicate that EDAR can make side-impact testing more reliable for piles whose tops are difficult to access, including foundations with missing records. Further work is needed to assess interference from other boundaries and extend the method to additional foundation types.

Keywords

Effective Dispersion Analysis of Reflections

EDAR

pile foundation length estimation

nondestructive testing

lateral hammer impacts

frequency-dependent phase difference

accelerometer sensors

wave dispersion model

pile tip reflections

concrete-filled steel tubes