Considering the viscous damping of the soil and the soil-pile torsional coupled vibration

regarding the pile as a one-dimensional rod and the soil as three dimensional axisymmetric viscoelastic medium

the frequency-domain torsional vibration response of cast-in-place concrete large-diameter pipe pile (PCC pile)in viscoelastic soil is theoretically investigated. The analytical solution in frequency domain is obtained by Laplace transformation method and the method of separation of variables. The solution is compared with the solution of a solid pile and plane strain solution extended to pipe pile to verify its rationality. Moreover

by analyzing the effects of pile length and viscous damping coefficient of soil on the velocity admittance and complex dynamic stiffness

the regularity of variations of the torsional vibration characteristics with parameters is obtained. Analysis shows that the complex dynamic stiffness at the top of pile increases with the increase of viscous damping coefficient of outer soil and the oscillation amplitudes of the velocity admittance decrease; while the effect of viscous damping of inner soil on the complex dynamic stiffness and velocity admittance is little. The complex dynamic stiffness increases and the oscillation amplitudes of the velocity admittance decrease with the increase of the pile length. However

when the pile length increases to a critical length

the effect trends to vanish.