Three-dimensional axisymmetric analysis of pile vertical vibration

Abstract

Widely used one-dimensional (1D) wave theory is not suitable to describe the wave propagation in the body of large-diameter piles under axial excitation. For large diameter piles, radial response of pile shaft could be substantial compared to its vertical response resulting in important 3D effect. This paper presents a rigorous three-dimensional axisymmetric (3DA) theoretical model to investigate the 3D effect during vertical vibration of an end-bearing pile embedded in homogeneous soil. Analytical solutions for the dynamic responses of pile points in both vertical and radial directions are deduced. The results indicate that traditional 1D wave theory overestimates the dynamic stiffness of the pile head, and high-frequency interference caused by the 3D effect of the pile body may lead to misinterpretation of the pile dynamic low strain tests. A new parameter, peak ratio, defined as the ratio of the peak radial response to that of the vertical response of a point, is proposed for evaluating the 3D effect of the pile body. Results demonstrate that peak ratios of specific points can be more than 30% for large-diameter piles, which implies substantial radial response during the vertical vibration and 3D effect is significant. It was found that there exist optimal locations with minimal high-frequency interference in the pile body, which should be chosen for monitoring the response for accurate interpretation of dynamic low strain testing of large-diameter piles.