Study On Bearing Behavior And Effective Length Of Super-long Piles In Soft Soil Area

With the rapid development of my country’s economy and the progress of construction technology,a series of super high-rise buildings and large bridges have emerged in my country.The superstructure of such buildings has strict requirements on settlement,and super-long piles are widely used due to their high bearing capacity and relatively small settlement.However,in the actual design and construction,in order to increase the bearing capacity and building reliability,the common method adopted by designers is to blindly increase the pile length.A number of subjects and experimental data have confirmed that there is an effective pile length problem for super long piles.How to determine the effective pile length of super long piles has become a key issue in design and construction.In this paper,the static load tests of super-long piles and the monitoring data of super-long pile groups in many soft soil areas are collected,and the bearing performance and effective pile length of super-long single piles and pile groups are analyzed through theoretical research and numerical simulation.A simple method for calculating the effective pile length of pile groups and analysis of its influencing factors.The content of the thesis is mainly divided into the following parts:(1)Using finite element software,the bearing performance of a single pile under vertical load was analyzed by means of displacement loading,and the effects of different pile lengths,pile diameters,soil elastic modulus,internal friction angle,and cohesion on the loadsettlement curve were explored.It is found that increasing the length and diameter of the pile can increase the bearing capacity of the foundation pile within a certain range.With the increase of the elastic modulus of the soil,the bearing capacity of the pile body also increases.The load-carrying performance is not significantly affected.The load transfer law of largediameter and super-long single piles is analyzed through the axial force curve of the pile body,the resistance curve of the pile side and the resistance curve of the pile end.A finite element method for determining the effective pile length is proposed,and the feasibility of obtaining the effective pile length by the finite element numerical simulation method and the effective pile length efficiency coefficient method is verified by comparing with the field measured data.(2)Based on the analysis of pile-soil interaction and pile-pile interaction by shear displacement method,the generalized load transfer method is adopted,combined with equilibrium conditions,the load transfer differential equation of super-long pile group is deduced,combined with the pile top pile of super-long pile According to the bottom boundary conditions,a calculation method for the settlement of the pile top of the super-long pile group is deduced,and through this method,a more accurate calculation method of the effective pile length is obtained.Compared with the elastic theory method and the normative method,it is closer to the measured data.(3)The finite element software is used to establish a three-dimensional calculation model of super-long pile groups in a homogeneous foundation,to explore the influence of the number of piles and pile spacing on the bearing performance of super-long pile groups,and to analyze the axial force distribution curve and lateral friction of side piles,corner piles and central piles.resistance distribution curve,study the load distribution law of super-long pile groups,put forward several judging methods for effective pile length,and compare and verify with multiple engineering examples,which proves the reliability of the finite element method and the theoretical method in this paper,which is practical Engineering design provides reference.