Lateral Nonlinear Dynamic Response Of Single Pile During The Passage Of Rayleigh Waves

For seismic excitation, analyzing soil-structure interaction consists of two distinct parts: first, determining the free-field response of the site, and second, calculating the modification of the seismic motion, the actual interaction, when the structure is inserted into the seismic environment of the free field. Far-field earthquake and environmental vibration are mainly caused by the Rayleigh waves. As an important structure, pile foundation has been widely used to consolidate soft ground because of its superior advantages. Therefore, study on soil-pile interaction during the passage of Rayleigh waves are important to the anti-seismic design of pile foundations. Current solutions concerning the lateral dynamic response of pile foundation during the passage of Rayleigh waves are mostly completed in the homogeneous half-space, linear viscoelastic and frequency domain. It cannot satisfactorily describe the nonlinear dynamic response of pile-foundation. In this dissertation, the lateral nonlinear dynamic response of the single pile are studied in layered soils, hysteresis nonlinear and time domain.First, determining the free-field response of the site during the passage of Rayleigh waves is necessary. The potential function and the FEM are introduced to derive dispersion equation for Rayleigh wave in layered soils. The dispersion equation consists of two forms: the IMPROVED-ANALYTICAL METHOD and the FEM-ANALYTICAL METHOD. Both methods have their distinct advantages and disadvantages. According to numerical characteristics of the dispersion equation, in the frequency-wavenumber domain(f-k domain), the BISECTION technique is employed to quickly and accurately search the roots of the dispersion equation. Thereby, the multimode dispersion curves of Rayleigh waves in variety of common layered soils are obtained and compared with that of the measured curves. On this basis, we studied the dispersion characteristics and displacement with depth attenuation characteristics for Rayleigh waves in layered soils.Secondly, the BWGG model is adopted to simulate the hysteretic nonlinear characteristics to the soil surrounding the pile. By calibrating against published experimental soil data and analyzing the related sensitivity of each parameter, the useful range of each parameter is bounded. Based on dynamic triaxial cyclical loading tests, the BWGG model is modified so that it is more compact and can reflect the influences of cyclical loading number N on the soil stiffness and strength weakened.Then, the BWGG model and the dynamic Winkler foundation model are employed to establish a newer simplified model which can truthfully reflect the main characteristics of the lateral nonlinear dynamic response of the single pile. Using Galerkin method to discrete dynamic equations, and adopting Newmark-β method to achieve the nonlinear dynamic response analysis for soil-pile interaction system in time domain. Proposed solutions are used to compare with the test data to verify the correctness and validity of the proposed method. Excellent agreements can be observed.Finally, the free-field dynamic response of the site during the passage of Rayleigh waves is applied as a boundary input to the soil-pile interaction model, and lateral nonlinear dynamic characteristics of the single pile is obtained. As an engineering example, this approach is applied for calculating the lateral nonlinear dynamic response of the single pile in SSRF site.