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 onedimensional 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