Three-Dimensional Effects in Low-Strain Integrity Testing of Large Diameter Pipe Piles

The interpretation of low-strain integrity testing performed on piles is commonly based on methods developed from the one-dimensional wave propagation theory. However, stress waves generated from the impact of the hammer on the head of a pipe pile propagate not only along the vertical, but also the circumferential and radial directions. One-dimensional methods that ignore these waves may underestimate the amplitude of the incident wave, and fail to predict the development of high-frequency interferences that may compromise the assessment of the integrity, particularly of large-diameter pipe piles. To account for these three-dimensional effects, the authors formulate a solution for determining the vertical vibration response along the cross-section of the pipe pile head to an impact load, which robustly accounts for coupling of pipe pile and viscoelastic soil vibrations. Presentation of the method is followed by a discussion on identifying the mechanisms that underlie body and surface stress-wave propagation along the section of the pipe pile head, and the conditions under which these may undermine the interpretation of pile integrity tests with conventional one-dimensional methods. A detailed parametric investigation revealed that there is an optimal position of the receiver, relative to the hammer impact, where the amplitude of the high-frequency interferences is minimized and the arrival of the reflected wave is clearly identified in the waveforms.