Dynamic Torsional Vibration of a Pipe Pile in Radial Heterogeneous Transversely Isotropic Saturated Soil

A rigorous theoretical solution is presented for torsional vibration response of a pipe pile embedded in radial heterogeneous transversely isotropic saturated soil. The method was successfully verified against the analytical solution to a pile embedded in transversely isotropic saturated soil and the analytical solution to a pile embedded in radially inhomogeneous saturated soil. The influence of the construction disturbance effect, the wall thickness of the pipe pile, and especially the soil transverse isotropy on the complex impedance, twist angle, and torque of the pipe pile in the frequency domain were investigated comprehensively. The results revealed that (1) if the influence of the soil transverse isotropy is neglected, the maximum deviation rate of both dynamic stiffness $K_T$ and dynamic damping $C_T$ can reach 40%, and may result in 25% underestimation and 40% overestimation of the twist angle at pile head, and 40% underestimation and 104% overestimation at pile midsection; (2) ignoring the effect of the construction disturbance, the overestimation rate of $C_T$ can reach 42% and 167% for $f=15$ and 30 Hz, respectively; and (3) using a solid pile to simulate a pipe pile with wall thickness of 0.01 m, the average underestimation deviation rate of $K_T$ would be 71% in the range 0–30 Hz, and $C_T$ would be underestimated by 82%–360%. The deviation rate of the twist angle at the pile top and the torque at the pile end were approximately 250%–320% and 1,900%–2,900%, respectively. The present solution is applicable for identifying various pile defects through torsional reflection analysis of pipe piles.