Abstract: In this study, a three-dimensional (3D) dynamical analysis is carried out for foundation piles under the action of a concentrated pulse load at the top centre by both in-situ test and numerical simulation. It is found that the amplitude of the envelope curve of velocity signal varies along the radial direction from point to point at the top plane of a pile. There exists a point where the amplitude of the envelope curve keeps the lowest, and this point is called 3D interference minimum point. The envelope amplitude decreases firstly from pile centre to this point and then increases outwards. The signals of 3D interference minimum points are compared with others in the literature. It is shown that the influence on the point location from pile-soil parameters such as pile diameter, pile length, load pulse width, elastic modulus of pile concrete, shear wave velocity and Poisson's ratio of surrounding soil, can be ignored. However, the point location is highly depending on the Poisson's ratio of pile concrete. The location of interference minimum point is more closed to the pile center when the value of Poisson's ratio of pile concrete is higher. A mathematical expression between the point location and the Poisson's ratio of pile concrete is then deduced, showing that the proposed method can be easily applied to practical engineering.

Key words: foundation pile, low strain integrity testing, three-dimensional analysis, interference minimum point, influence factor