A rubber-coated bored pile in isolating metro-induced vibrations: Concept, analytical and in-situ investigation

For the buildings with pile foundations adjacent to or even right above the metro tunnels, mitigation measures in isolating the metro-induced vibration propagation along the pile become necessary to reduce annoyance to residents. To achieve this goal, a novel vibration isolation measure concept of the rubber-coated bored pile (RCBP) is proposed in this paper. An analytical solution is deduced to investigate the dynamic impedance of the pile. A field application of the RCBP is presented, along with two in-situ tests conducted for metro-induced vibration and pile head dynamic stiffness. The results confirm the dominant frequencies of the metro-induced dynamic response at the pile head is highly related to its dynamic stiffness. The influence of the rubbercoated layer is further examined by a parametric study in which the analytical and the numerical solutions are both of consideration. It is demonstrated that the effect of the variation of the rubber-coated layer thickness is negligible in engineering practices, while the variation of the rubber-coated layer depth has a significant impact on both the dynamic stiffness and the dynamic response at the pile head. Results from the in-situ test, analytical and numerical solutions confirm the potential of the rubber-coated bored pile in isolating metro-induced vibrations.