Abstract：The Beam-on-Dynamic-Winkler-Foundation (BDWF) model is utilized to determine the lateral dynamic response of single pile in viscoelastic subgrade. Based on frequency-dependent stiffness and damp coefficients，and with the pile modeled as a Timoshenko beam considering both bending and shearing，a more rigorous analytical solution on lateral vibration of a single pile is developed. By comparing the presented theory and that based on Euler beam model，the critical length of pile in homogeneous soil is obtained by modeling the pile as a Euler beam. In most cases, this critical length is about 8 times diameter of pile and it is nearly independent of dimensionless frequency and the ratio of Young’s modulus of the pile to that of the soil. It is also found that neglecting the shear deformation of pile will lead to a relatively smaller calculation result，which is not safe in engineering application.
