The Bearing Behaviors Of Vertically-loaded Single Floating Pile In Multilayered Soil By Thin Annulus Element Method

The pile foundation has many advantages,such as high bearing capacity,small and even settlement,convenience for construction and universal applicability.Thus,it has been widely used in engineering practices,such as high-rise buildings,high-speed railways,bridge engineering,dynamic foundation design of factory buildings and seismic design of buildings.As important control parameters of pile foundation design,the bearing behaviors of piles under axial working loads have been widely concerned.A lot of researches and studies about this area have been obtained.The study of pilesoil interaction under vertical dynamic and static loads enables people deepen the understanding of the bearing characteristics of piles.Meanwhile,it can also provide theoretical guidance for engineering practice and design.Therefore,the study of pilesoil interaction is of significance in both theory and practice.On the basis of extensive literature investigations,the presented paper established a thin annulus element model for the calculation of the bearing capacity of single floating pile in multilayered foundation.The main contents and achievements of presented paper are:(1)To consider the displacement the load transfer of vertically loaded floating piles in layered foundation,a thin annulus element model and its corresponding semi-analytical method is proposed in presented paper.Firstly,based on the hypothesis of fictitious soil pile,the pile-soil system is divided into separate thin annulus elements.Then,the stiffness matrices for the soil element and the pile element can be established by using the virtual displacement principle.The global matrices can be deduced according to the equilibrium and continuity conditions between the elements.Finally,the displacement field of the pile-soil system can be determined by solving the global matrices.The results of presented model agree well with the existing solutions and test data in literature,which verifies the accuracy and reliability of the model.The bearing behaviors of vertically loaded floating pile in multilayered foundation is examined in presented paper applying the thin annulus element model.The parametric analysis shows that for the floating pile in three-layered soil,the parametric studies show that the rise of the middle layer will significant increase the shaft resistance of the middle layer and the stiffness of pile top.The pile tip stiffness increases when the distance between the pile tip and the bedrock decreases.(2)Considering the wide application of piles in the dynamic machinery foundations,presented paper also investigate the bearing characteristics of dynamic axially loaded pile by thin annulus element method.Firstly,the thin annulus element model is used to divide the pile-soil system into separate elements.The stiffness matrices with inertia term is established by the Hamilton principle.Then,according to the equilibrium conditions between elements and the boundary conditi ons of the pilesoil system,the global stiffness matrices can be constructed and solve.Finally,the displacement field of the pile-soil system can be obtained.The investigation into the floating pile under harmonic excitations shows: under the high frequency axial loads,the complex stiffness at the pile top varies with the variation of the slenderness ratio of the pile.The shaft resistance will magnify with the increase of excitation frequency once the frequency exceeds the cut-off frequency.A thin annulus element method is proposed in presented paper.The method can be utilized to analyze the bearing capacity and displacement characteristics of floating piles in multilayered soils.The method is of simplicity,efficiency and engineering application value.The larger the slenderness ratio,the larger complex pile top stiffness of floating piles under high frequency load.The stiffness of pile tip is examined and the application of a rigid disc on elastic half-space is discussed in this paper.