Study On Soil-Pile Interaction In Longitudinal Vibration Considering Vertical Wave Effect Of Soil

On the basis of three-dimensional axially symmetrical soil model and taking consideration of vertical wave effect of soil layer, the interaction between visco-elastic layered soil and an integral pile or a multi-defective pile with arbitrary bottom boundaries and its engineering application is systematically studied in this dissertation. The main original work includes:1. The interaction between an integral pile and a uniform visco-elastic soil layer with viscous damping or hysteretic damping is theoretically studied, and the pile response to a harmonic load is obtained in a closed form and used to define complex stiffness at the pile head. Semi-analytical solution of the velocity response in time domain subjected to a semi-sine wave exciting force is also given. Based on these solutions, a parametric study is conducted to determine the main features of the soil-pile system vibration, and the special influence of viscous damping of soil layer around pile is discussed. It indicates that viscous damping of soil layer shows a clear different effect on dynamic response at pile head comparing to hysteretic damping.2. The complex stiffness corresponding to three bearing conditions of semi-infinite elastic subgrade, finite elastic soil layer and end bearing at the pile bottom are theoretically investigated, and analytical expression of the complex stiffness corresponding to finite elastic soil layer bearing condition is obtained. The special influence of bearing conditions on dynamic response at pile head is then discussed.3. By comparing the available theories corresponding to plane strain model and Winkler model with the solutions developed in this paper, the applicability of the two models is analyzed and checked. The comparison involves many aspects such as local soil stiffness, dynamic stiffness and time domain response at the pile head, and some important conclusions are made.4. With the consideration of the vertical wave effect of soil and soil-pile interaction, an approximate analytical solution to vertical vibration of pile system with variable impedance in visco-elastic layered soil is developed. A simplified and practicalmathematical model for interaction between soil layers is proposed, and its applicability is theoretically investigated . Based on this model and by using Laplace transforms and the transmit property of impedance function, the analytical expression of the impedance function and solutions of the displacement and velocity response function in frequency domain and in time domain at the pile head are derived.5. Based on the solutions developed herein , the main features of the interaction between visco-elastic layered soil and an integral pile or a multi-defective pile are systematically analyzed. The influence on the vibration properties caused by soil modulus, the degree of pile defects, and the length and location of the defects are discussed, and many important conclusions are drawn.6. By making the comparison of the new theory developed in this dissertation and other theories for pile vertical vibration, the correctness and applicability of the new theory is verified. Meanwhile, the fitted curves of analytical solutions are compared with the field measured ones, and it is proved that the theoretical curves are in good agreement with that obtained from the field measurement.In comparison with other theories, the theoretical solutions presented herein for longitudinal vibration of soil-pile system is more rigorous and reasonable in theory, and more reliable and applicable in use. This not only makes the theory of pile vibration more perfect, but also provides a totally new theoretical support for pile foundation seismic design and pile dynamic testing.