Horizontal Dynamic Response Of Piles And Pile Groups In Saturated Soil

With the advantages of small settlement, good seismic performance and large capacity, pile has been widely used in many engineering fields like bridges, high-rise building and offshore platforms. The stability of the pile foundation is related to its field performance, which is depend on the interaction between the pile and the surrounding soils. At present, the dynamic response of partially embedded piles and the transient response of piles are limited in single-phrase medium, while natural soil is combined by soil grain, water and air, and most geotechnical materials are in a saturated or quasi-saturated state and layered distribution. Therefore, it is important and of practical significance to study the horizontal dynamic response of piles and pile groups in saturated soils to ensure the safety and stability of structures. Supported bythe specialized research fund for the Doctoral program of higher education of China and other program funds, the horizontal dynamic response of high capped pile foundation and the horizontal transient response of piles have been studied in this paper.In this study, the soil around the pile is regarded as saturated porous medium. Based on Biot’s three-dimensional wave theory, the horizontal fundamental solutions in half space is obtained by Novak thin-layer method. The matrix equations to describe the stiffness of the pile are deduced from continuity condition (the continuity of displacement, rotation, shear force, bending moment of element ends) of pile element and the compatibility between the pile and the soil. The horizontal impedance and the bending moment of single pile is obtained by employing boundary conditions. Besides, the existing lateral displacement of the half space saturated soil is introduced to build the attenuation function, and the balance equation of passive pile is built accordingly. Then, the built balance equation of the passive pile is solved using simple Winkler model from which the pile-soil-pile dynamic interaction factor is deduced. Finally, the horizontal impedance of pile group is obtained by solving the matrix equation deduced through superposition principle. Main parameters like embedded ratio, pile separation distance, modulus ratio of layered soil and permeability are calculated numerically.The Biot’s consolidation equation is first nondimensionalized and Laplace transformed, then the potential function is introduced to decouple the governing differential equation. By means of differential operator splitting and variable separation method, the displacement of saturated soil is obtained. Based on the displacement of the saturated soil, the attenuation function in Laplace domain is builded. Coupling with the lateral vibration differential equation of pile foundation, the expression of the horizontal displacement of single pile and pile group and the internal force of the single pile in Laplace space is obtained. The closed solution of displacement of the pile is calculated by usingan optimal model of numerical inverse Laplace transforms. Parametric studies have been carried out and it is found that the influences of pile-soil stiffness ratio, slenderness and permeability are significant to single pile. Besides, pile-soil stiffness ratio pays a critical role in bending moment and shear force and their distribution.