Study On The Coupled Vibration Of Large Diameter Pile And Non-homogeneous Soil

Due to their higher bearing capacity and smaller settlement deformation, Large-diameter piles are widely used in large-scale projects such as high-rise buildings, road engineering, bridge engineering etc. While the working characteristic can not be learned from previous pile foundation theories because of their special geometric size. At present, studies on dynamic property of large-diameter plies are even more deficient than that on static property.Based on current research status, study on vertical vibration of large-diameter pile is carried out in this paper. On one hand, simplified models of pile body, interaction of pile and pile-side soil, pile and pile-end soil are applied to study the vertical vibration of large-diameter pile in homogeneous and non-homogeneous soil respectively. On the other hand, numerical simulation by FEM is conducted and the numerical solution is obtained to verify the feasibility of numerical analysis. The specific contents of this paper are as follows:(1) Based on the plane strain model and Rayleigh-Love bar model, the vertical vibration of large-diameter pile in homogeneous soil is studied under the condition of viscoelastic support. The analytical solution of frequency domain response and semi-analytical solution of time domain response of the pile top are derived by integral transformation method. And based on the theoretical solution, the characteristic parameters of large diameter piles are analyzed such as Poisson's ratio, diameter, pile length, longitudinal wave velocity and so on.(2) The diffused fictitious soil pile regarded as one-dimension bar is substituted for the viscoelastic supporting model of pile-end soil to study the vertical vibration of large-diameter pile in radial heterogeneous soil. The theoretical solutions are derived by the integral transform method and the impedance function recurrence method. And the analysis on effects of the characteristic parameters of diffused fictitious soil pile such as dividing precision, fictitious soil pile length, diffusion angle and longitudinal wave velocity on the dynamic responses of pile top are studied.(3) Considering the effect of radial disturbance caused by construction and Vertical stratification of pile side soil, study on the vertical vibration of large-diameter pile in non-homogeneous soil is furthered based on diffused fictitious soil pile model and the multi-zone plane strain model with complex stiffness transfer. Theoretical solution of dynamic response of pile top is obtained by means of the cyclic shear complex stiffness transfer method and the impedance function transfer method. The influence mechanism of radial disturbance degree, disturbance range, vertical hardening(softening) interlayer and the density of pile side soil on the vibration characteristics of large-diameter pile is studied by the method of parameter analysis.(4) ANSYS/LS-DYNA is applied into model establishment and numerical analysis of pile-soil vibration on different wording conditions:changes in length of fictitious soil pile, changes in size of large-diameter pile, vertical hard(soft) interlayers in pile side soil and radial hardening(softening) disturbance of pile side soil. Related velocity-time curves on pile top are obtained to study the change regulation. Meanwhile, the numerical solutions are compared with theoretical solutions to verify their feasibility.(5) In the end of this paper, some useful conclusions are summed up. Also the defects of the study and improvements needed are pointed out to prospect for the further study in this field.