Propagation characteristics of flexural wave and the reflection from vertical cracks during pipe‐pile integrity testing

Abstract

The propagation characteristics of F-(flexural) wave and the reflection from vertical cracks in pipe-piles subjected to an eccentric vertical excitation were numerically investigated using elastodynamic finite integration technique (EFIT). The accuracy of the self-written code was validated by comparing computed results against the measured data. The snapshots of circumferential, radial and vertical velocities in intact and cracked pipe-piles, as well as the velocity histories of the pile-top were presented. It is found that not only L-(longitudinal) wave (corresponding to axisymmetric mode) but also F-wave (corresponding to nonaxisymmetric mode) can be excited in pipe-piles subjected to an eccentric vertical excitation. F-wave causes motion in all directions, while L-wave only causes vertical motion. The three-dimensional (3-D) interference is weak at 90 • away from the excitation position for circumferential velocity response, while at 45 • or 135 • for radial velocity response. The reflected F-wave (RFW) from the pipetoe has multiple peaks due to the dispersion effect of F-wave. Reflection occurs when F-wave encounters vertical cracks, while L-wave is not sensitive to vertical cracks. The intensity of RFW from vertical cracks varies with excitation-andsensor modes. For shallow vertical cracks, the RFW strength varies with the sensor positions; while the intensity of the RFW caused by deep vertical cracks varies little with the sensor positions. With the increase of crack length, the strength of the first arrival RFW due to the vertical crack has no obvious change; however, the strength of RFW from the pile-toe decreases.

Torsional Low-Strain Test for Nondestructive Integrity Examination of Existing High-Pile Foundation

“…The torsional vibration theory is initially established on a similar basis to the longitudinal one: by simplifying the soil medium to infinitely thin layers, the rigorous 3D continuum theory for soil medium can be reduced to the plane strain model, based on which the straightforward closed-form solutions can be derived [ 25 , 26 , 27 , 28 , 29 ]. As the torsional vibration of pile foundations gained interest in the most recent decade, the finite element method (FEM) [ 30 , 31 , 32 ], finite integration technique [ 33 ], and boundary element method [ 34 , 35 ] all considerably fulfilled the knowledge of wave propagation across the soil-pile system during vibration.…”