Longitudinal Vibration Theory Of Pile In Layered Soils And Its Application In PIT

Longitudinal vibration theory of pile is the basis of any kind of method in dynamic pile testing, which can be used to explain the dynamic reaction between pile and soil, the mechanics of pile testing, and to illustrate the pile testing curves.In this dissertation, on the basis of the existing work, the longitudinal vibration properties of the pile with defects in layered soils have been studied with a totally new approach. The main original work includes:Firstly, it is necessary to study the vibration behavior of pile in layered soils since layered property is one of the main characteristics of soil stratum. With Laplace transforms, the analytical expression of the impedance function is derived for the pile in layered soils subjected to an exciting force at its top. Then a semi-analytical solution of the velocity response in time-domain under semi-sine exciting force is given. Based on the solutions, the influence of soil modulus on the dynamic stiffness and the dynamic-damping of the system of pile and soil, and that on the curves of mechanical admittance and the reflection wave of pile are analyzed. In order to explain the response curves of pile correctly, the curves corresponding to soil modulus varying are compared with the ones corresponding to defective pile.Secondly, since the main objective of performing dynamic pile testing is to evaluate the integrity of drill shafts definitively, the study is focused on the vibration properties of defective pile. The defective piles fall into two categories according to the causes they formed: one is the pile with variable sections, the other is the pile with variable modulus. In the dissertation, a semi-analytical solution for a pile of arbitrary segments with variable section area and an analytical one for a pile of arbitrary segments with variable modulus are derived respectively. The solutions are then extended in a semi-analytical form to the defective pile with arbitrary segments in layered soils. Using these solutions, the influences on the vibration properties caused by the degree of pile defects, the length and the location of the defects, the exciting frequency and the damping of pile material are studied. Comparison is also made for the vibration properties of the pile with variable section and the'one with variable modulus. Furthermore, to verify the theory developed herein, the fitted curves of analytical solutions are compared with the field measured ones, which shows that they are in a good agreement.Finally, by means of 3D finite element method, the influence of "3D effect" on the vibration properties of the defective pile is studied, and the difference of vibration properties between the pile with un-axial defect and the one with axial defect is compared. Moreover, the result obtained from 3D FEM and the one from ID analytical solution developed in the dissertation are compared.