Torsional Dynamic Response Of A Pipe Pile In The Heterogeneous Saturated Soil

Due to the advantages of convenient construction,high bearing capacityand reliable quality,the pipe pile has been widely used in various offshore construction foundations.Compared with solid piles and other pile types,the force mechanism is more complicated because of the joint action of pile surrounding soil and pile core soil.The pipe piles are often subjected to various loads during service,when the load is eccentric or the pile body does not have a symmetry plane,the pile foundation will undergo torsional deformation.Even if it is a symmetrical structure,it will occur under the excitation of the rotational component of the ground motion.These all make the effect of the torque on the bearing performance of the pile foundation not negligible.At present,the study on the torsional dynamic response of pile foundations is mainly focused on solid piles.The research on torsional vibration of piles under complicated conditions is still relatively limited,and it is necessary to carry out research on them.This article is divided into five chapters,mainly to do the following work:1.Through summarizing a large number of literatures,the research status of pile foundation torsional dynamic response at home and abroad is summarized from four aspects: solid pile,pipe pile,special-shaped pile and group piles.And research methods and problems of pile foundation considering factors such as flexible constraints of pile top and heterogeneous soil have been summarized.Added to this,the advantages and disadvantages and applicability of existingVI research results are discussed.2.An analytical solution is developed to investigate the torsional dynamic response of an end bearing pile embedded in heterogeneous saturated soil with a flexible support at pile head.The torsional dynamic impedances of the outer and inner soil are first solved based on Biot's motion wave equation and the Novak's thin layer method.The torsional dynamic response and complex dynamic impedance of the pipe pile are then deduced by discretizing the dynamic equation of pipe pile into difference schemes.The obtained solutions are degenerated to the frequency domain solutions of a solid pile and a pipe pile,and compared with the existing literature,the rationality of the solutions is verified.The influence of various parameters on the dynamic impedance of pile top in frequency domain is analyzed by mechanical parameters.3.Torsional vibration of an end bearing pipe pile embedded in layered saturated soil and subjected to a transient torsional loading is theoretically investigated.Firstly,the interaction between soil layers is simplified into a series of distributed linear springs,and a simplified model of layered saturated soil is proposed.The Biot's wave equation is decoupled by using Laplace transformation and variables separation.By utilizing the boundary and continuity conditions of the pile-soil system,the dynamic response of each segment of pipe pile is further obtained in transformation domain.Then,by using the recursion of the impedance functions and the inverse Laplace transformation technique,the time domain solutions of the transient torsional response of the pipe pile in the layered saturated soil is derived.The obtained solutions are compared with the existing literatures,and the rationality of the solutions is verified.The influence of various parameters on the dynamic impedance of pile top in time domain is analyzed by numerical examples.4.An analytical solution is developed to investigate nonlinear torsional vibration of a pipe pile in radial heterogeneous saturated soil.Based on theradial heterogeneous soil model,the pile-soil system of transversely isotropic saturated soil is established,which the soil is nonlinear due to the disturbance of dynamic loads.The equivalent linear model is used to simulate the non-linear effect of soil.Based on Biot's wave equation,the governing equation of pile-soil system with rigid support at the end of pile is established.Then,the soil equation is solved by using separation variable method,and the displacement form solution of the soil is obtained by using the boundary and continuity conditions of the radially inhomogeneous soil layers and means of transfer of coefficient.Combined with the displacement and stress continuity conditions of pile-soil interface,the torsional vibration response of pipe pile in frequency domain is further obtained,and the solutions of pile top impedance are obtained.It is assumed that the obtained solution is reduced to three cases,i.e.considering only the radial heterogeneity of the soil around the pile,the nonlinear effect of the soil and the transverse isotropy.The rationality of the solution is verified by comparing with the existing literature.A parametric study is conducted to investigate the influence of mechanical parameters on the torsional vibration characteristics of the pipe pile.