Research Of Influencing Factors Of Pile Dynamic Stiffness At Low Strain Testing

For the study of pile dynamic stiffness influencing factors, the mostly used simulation methods are finite element method, analytical or semi-analytical solution method and difference method. In this paper, a three-dimensional axisymmetric pile-soil model was established, and finite difference method was used to obtain the numerical solution of pile-soil vertical vibration cases. Then method of numerical solution was applied to simulate engineering piles, and the results were compared with the measured curves, which verified the correctness of this numerical calculation. Fast Fourier Transform was used to get the vibration velocity amplitude spectrum |V(f)|. Under the known condition of impact force amplitude spectrum|P(f)|, speed admittance curve|H(f)|of pile-soil system was obtained via equation|H(f)|=|V(f)|/|P(f)|. Then calculation formula Kd=2πf/|H(f)|was utilized to obtain pile dynamic stiffness.Pile-soil parameters were changed to calculate transient dynamic response at pile top under different datum. Pile dynamic stiffness values and variation trend curves corresponding different parameters were obtained, and the influences of pile defects, pile body, surrounding soil, bottom soil were studied. The results showed the circumstances when pile-soil parameters were changed to improve pile-soil strength made pile dynamic stiffness increase, and vice versa.The variable cross-section pile and three-dimensional viscoelastic pile-soil model were also simulated and calculated. Different variable cross-section pile dynamic stiffness values were compared. Influence of viscosity to pile dynamic stiffness was expressed at the end of this paper.