Analysis Of 3D Dynamic Effect On The Top Of Piles

Low strain dynamic test method is the most representative and popular way of pile integrity testing presently. It has been generally accepted for its virtues such as portability, celerity, economy and high veracity. However, results of low strain integrity testing of piles are normally interpreted using one-dimensional (1D) stress wave theory. While 1D stress wave theory is acceptable for pile-driving analysis, it may not adequately simulate the response of piles integrity tests when the hammer and the incident wave length are small in relation to the diameter of the pile. In fact, in this situation piles integrity test is really a 3D problem. Because of the 3D dynamic effect, it has difficulty estimating big diameter piles and piles with superficial defects.In this paper, stress wave in 3D space, stress wave's inclined reflection and the theoretical explanation of 3D effect are introduced. Considering calculating precision and efficiency, the axial symmetry system of COMSOL Multiphysics is used to simulate the process of pile's dynamic testing. The dynamic response curves of an intact pile in 1D and 3D are calculated. The main 3D effect lies in the oscillating degrees of velocity curves and the time of reflected wave. Under the condition of different hammer, wave length, pile diameter, the 3D dynamic effect is analyzed and some suggestions about how to avoid it are put forward. Moreover, further studies of piles integrity test such as"influence depth", form of direct spherical wave are analyzed in this paper.The results of the paper can be used as the instruction of pile integrity testing. It also can be used to correct some wrong opinions and to prepare for the work of torsional wave and frequency analysis.