Inclination correction of the parallel seismic test for pile length detection

An inclination factor is proposed in this paper to enhance the accuracy of the parallel seismic method for pile length assessment when a borehole is not drilled perfectly parallel with the tested foundation. Three-dimensional axisymmetric finite element models were performed to show the effects of the inclined angles of the borehole. A series of parametric studies, including the pile length, the borehole distance, and the wave propagation velocity of the soil, were also carried out to investigate their effects on the derived modified factor for pile length prediction. The results from the numerical models show that the estimated error (5-20%) of the pile lengths increases with the increasing inclined angles, and can be reduced to less than 5% when the derived inclination factor is considered. In addition, the slope of the top fitted straight line in the first arrival time versus depth plot does not represent the true P-wave velocity of the tested structure if the borehole is not perfectly parallel with the pile foundation and use of this value to determine the quality of the tested pile foundation would be unsuitable. However, this unreasonable value of the P-wave velocity of the tested pile can be used as a guide, representing the inclination of the borehole.