Pile Length Estimate of Impulse Response Testing with Guided Wave Approach
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RESEARCH PAPER
Pile Length Estimate of Impulse Response Testing with Guided Wave Approach Helsin Wang 1 Received: 31 July 2019 / Accepted: 23 May 2020 # The Society for Experimental Mechanics, Inc 2020
Abstract The constant velocity one-dimensional wave theory has been commonly used to determine the pile lengths from the impulse response testing results for several years. In this paper, the three-dimensional guided wave theory was introduced to extract more information from the impulse response spectra on five concrete piles. Combined with resonance concept, this guided wave-based approach was developed to simply and efficiently identify the length estimates with 3% or less errors, similar to those of the conventional one-dimensional wave-based approach. Moreover, the guided wave theory provides more individual resonant frequencies insight over that of the one-dimensional wave theory. All the experimental phase velocities at their corresponding resonant frequencies have a good consistency with the guided wave prediction curve at frequencies up to 5000 Hz. The resulting scattering also presents a slightly decrease trend with frequency. The overall analysis indicates that the guided wave theory can give more useful information than that of the one-dimensional wave theory. In future, one can use this inverse computation approach to evaluate unknown pile lengths. Keywords Impulse response . Guided wave theory . One-dimensional wave theory . Resonance . Pile length estimate . Resonant frequency
Introduction Integrity testing plays a critical role in the quality control or quality assurance of drilled shafts and concrete piles, which may support civil infrastructures, for example, bridges or temporal retaining walls [1–4]. The integrity evaluation consists of the geometrical dimension, continuity, and consistency in deep foundations. Traditionally, identifying the dimension, especially length, of deep foundation is the key concern for most investigators [2, 3, 5]. These inspection outcomes can provide substantial information for civil engineers to evaluate the structural stability and safety, if no foundation information available. In the past few years, the impulse response technique has been extended to inspect as-built conditions on anchor rods, soil nails, tunnel lining, pavement, and stone retaining walls for slope stability purpose in geotechnical practice [6–10].
* Helsin Wang [email protected] 1
HCK Geophysical, 9F-3, No.79, Section 2, Roosevelt Road, Taipei 10646, Taiwan
The one-dimensional (1-D) wave theory is intuitively assumed to interpret the impulse response testing results in drilled shafts or concrete piles [1, 11]. The proposed 1-D or plane waves are propagating forward and backward between the pile top and bottom in the longitudinal direction. The wave velocity is considered as a constant and does not change with frequency. The cross-sectional displacement response is postulated uniform along the direction of propagation, and the wavelength is much larger than the diameter of the pile [11–13].
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