Influences of soil plug effect on apparent wave velocity of pipe piles during low-strain integrity

First, the analytical solution in the frequency domain for the vertical dynamic response of pipe piles is established based on the additional mass model with the consideration of wave propagating both in the vertical and circumferential directions. Then, the corresponding quasi-analytical solution in the time domain for the pipe piles subjected to a vertical semi-sinusoidal impact force is obtained by utilizing the Fourier transform technique. Finally, based on the derived solutions, the influences of soil plug effect on the apparent wave velocity of pipe piles (AWVPP) are investigated. The proposed theory can provide a more precise AWVPP calculation basis for the low-strain integrity tests on pipe piles. The rationality and accuracy of the proposed solution are verified by comparing the fitted curves of the current solution with those based on previous theories and a series of model pipe pile experiments and field tests. The result shows that the reduction degree of AWVPP due to the soil plug effect increases with the decrease in wall thickness and vertical stress wave velocity of the pipe piles. Owing to the soil plug effect, the width of the reflected signal from pipe pile toe is widened, and its arrival time varies as the receiving acceleration transducer moves along the circumferential direction of pipe pile head.