The Influential Factors Research To Low Order Resonant Frequency Of Three-dimensional Pile

For the traditional research theory of low order resonant frequency of pile, theinfluences of rock and soil around the pile and at the bottom are simplified toequivalent parameters under one-dimensional condition. In this paper, theaxisymmetric model of pile-soil system is established. The speed curve v(t) at pile topis obtained via using staggered grid finite difference method to solve definite solutionproblem, and the vibration velocity amplitude spectrum|V(f)|is got by using the fastFourier transform. Speed admittance curve|H(f)|of pile-soil system is obtained viausing equation|H(f)|=|V(f)|/|P(f)|when the impact force amplitude spectrum|P(f)|isknown. The resonant frequencies of pile are got by using velocity amplitude spectrumor speed admittance curve. The fitting analysis between the numerical results fromengineering pile and the measured curve has been made to verify the correctness ofthe numerical calculation.Given different parameters of pile-soil and impact force, the frequency-domaincharacteristics of pile under three-dimensional condition are obtained by calculatingthe transient dynamic response of three-dimensional model of pile. Time-domainvertical vibration velocity curve at pile top, velocity amplitude spectrum curve andspeed admittance curve are plotted according to the calculation data. Low order(mainly first and second order) resonant frequency characteristics of pile underthree-dimensional condition are discussed and compared with one-dimensionalanalytical solutions.The influences of rock-socketed depth and sediment thickness of rock-socketedpile in three-dimensional axisymmetric model on low order resonant frequency arealso discussed in this paper. The results show that under certain fixed conditions, thefirst and the second order resonant frequencies of the measured dynamic test curvecan be used to accurately deduce the parameters of soil at the bottom and the qualityof rock-socketed pile, and the accuracy of evaluating rock-socketed pile bottom bylow-strain method is also improved.