Semi-analytical approach for nondestructive test for offshore pipe piles considering soil-pile slippage induced by heavy hammer impact

For the offshore large dimension piles, heavy hammer impact is often utilized as the input of the incident wave of the low strain integrity test, making the slippage at the soil-pile interface inevitable. Also, the significant soil plug effect and the transverse inertia effect associated with the large dimension pipe piles bring severe challenges to the test signal processing. To facilitate signal interpretation, this paper establishes a rigorous saturated seabed -pipe pile-soil plug mathematical model, pioneering the coupling analysis of the soil plug, transverse inertia, and the soil-pile slippage effects, which usually occur simultaneously for offshore pile testings. The soil-pile slippage is realized through distributed linear viscoelastic springs and dashpots. The main findings can be summarized as: 1. The increase of the strength (both stiffness and damping) at the soil-pile interfaces would decrease the am-plitudes of the reflected signal. 2. The increases in the wall thickness and the Poisson's ratio of the pile both increase the wave oscillation after the reflected signals. 3. As the degree or the length of the defect increases, the amplitude of the reflected signal of the corresponding defect would increase, whereas the amplitude of the re-flected signal at the pile bottom would decrease in the opposite.