Simulation Analysis Of Vibration Source Characteristics In Piles' Dynamic Test

Among all the influencing factors during the pile integrity test, the vibration source is the one of great importance that may to some extent determine the effect of the testing results. For the research on the characterization of the vibration source, the need for systematic theoretical analysis and numerical simulation has been greatly driven by their absence, since most of the research was previously conducted by the in-situ and laboratory experiments. In this thesis, numerical simulation has been conducted by the software package ANSYS/LS-DYNA to study the vibration source characteristics for both the integral and defect piles, and conclusions have been made for the matching properties between the hammer and the pile.An analytical solution was deduced for the pulse of the stress wave that initiated by the hammer, and this solution was then qualitatively analyzed when varying different influencing factors. In addition to the analytical analysis, numerical modeling was carried out by simulating the harmer striking process, the result from which was subsequently compared with the previously deduced analytical solution and found to be no statistical difference, suggesting the validity of this model. By taking the soil effect into consideration, this validated model was firstly adopted to study the integral pile on its vibration source characteristics and matching properties between the hammer and the pile, during which a variety of factors that may influence the matching properties were studied, i.e., the striking velocity of the hammer, the thickness and stiffness of the hammer mat, the length and diameter of the pile, and the pile-soil interaction. Basing on these studied factors and together with the analytical solution, corresponding rules and suggestions for the hammer selection were proposed. The model with the soil effect taken into consideration was secondly adopted for defect piles, including single, multi and small shallow defect piles, to examine their vibration source characteristics and matching properties between the hammer and the pile. Finally, this model was used to investigate how the varying lengths of defects along radial and axial directions influence the matching properties between the hammer and the pile.In this thesis, vibration source characteristics and its matching properties with the pile during the pile integrity test was studied in certain depth, which may be beneficial for further theoretical research and engineering practice.