Dynamic impedances and free-field vibration analysis of pile groups in saturated ground

• Green function of three-dimensional saturated ground is obtained and verified.
• Impedances of pile groups embedded in saturated ground are obtained.
• Free-field displacement and pore pressure responses are analyzed.

A three-dimensional (3D) numerical model basing on the thin layer element method and the flexible volume method was established for the computation of dynamic impedances and free-field vibrations of rigidly-capped pile groups embedded in saturated ground. The piles were considered as beams and the saturated ground was represented by Biot׳s three-dimensional elastodynamic theory. By recourse to the thin layer element method, Green function of the three dimensional saturated ground was obtained and then verified. The dynamic interaction of the piles and the saturated ground was solved by using the flexible volume method, in which the piles were discretized into three dimensional Euler−Bernoulli beam elements and the dynamic stiffness matrix of saturated ground was formed at the pile−soil interaction nodes by using the Green function. Impedances of the 2×2 pile group and free-field displacement and pore pressure responses caused by harmonic vertical, lateral and rocking forces (moments) applied at the cap center were presented, respectively, for different soil permeability and excitation frequencies. It is found that the soil permeability and the excitation frequency have significant influence on the impedances and the free-field vibration responses.