Vertical vibration of partially embedded pile groups

A simplified analytical method is developed for the axial harmonic response of partially embedded pile groups in homogeneous and non-homogeneous soil deposits.Based on pile-to-pile interaction factors,the transfer matrix method is used to establish the dynamic model of partially embedded pile groups,while the pile is treated as dynamic Winkler beam.A comprehensive parameter study focuses on the influence of length ratio(L1/ L2),pile spacing(s/d) and vibration frequency(f) on the dynamic response of pile groups,and the following conclusions can be drawn:① the increase of length ratio(L1/ L2) will reduce the vertical dynamic impedance of a single pile and pile groups;② the pile-pile interaction factors vary with the pile spacing and vibration frequency,and will be seriously weakened due to the existence of length ratio(L1/ L2);③ the length ratio(L1/ L2) has little influence on the dynamic response of pile foundations in low frequency,but it will be more and more evident with the increase of vibration frequency.And this approach is verified by comparing field test results.Finally,the present model is used to predict the vertical dynamic vibration of a pile foundation of an offshore platform.