| A new type of variable cross-section pile has emerged in recent years.Its squeezed branch and plate piles are used to squeeze the soil around the pile into a plate through hydraulic squeezing equipment,forming a friction end bearing pile with the combination of the pile and the bearing plate.Applying the vertical load on the top of the pile with pile side,bearing plate and pile end,endows the branch piles a series of advantages such as higher bearing capacity and smaller settlement,which makes it becomes more popular than the equal diameter pile.At present,the load transfer mechanism and bearing deformation characteristics of a single squeezed branch and plate pile have been studied in detail.However,pile group foundations are often used in actual projects.Therefore,the study of extruded support disc group pile is very necessary.For group pile foundation,the settlement of pile top and settlement difference are the two aspects to be focused on.For small-scale group pile foundation,when there is a site and other factors to limit its pile spacing,it will make the neighboring pile bearing discs affect each other,increasing the pile perimeter soil stress superposition,weakening the bearing performance of the bearing discs,resulting in the reduction of the group pile bearing capacity,and the settlement increases.For large-scale piled raft foundations used in high-rise buildings,the traditional equal-rigidity pile arrangement method will gradually reduce the vertical support stiffness of each pile from the outside to the inside due to the pile group effect,and the foundation will show a difference in saucer-shaped settlement.For high-rise buildings with a frame-core tube system with uneven load distribution,the difference will be more obvious.In view of the above problems,this article uses the finite element method to study the working performance of the squeezed branch pile group under vertical load firstly,and then the refines settlement and settlement difference involved in two types of squeezed branch pile group respectively.The main contents and results are depicted as follows:(1)Establish a 3×3 extruded support disc group pile model,analyze its load bearing characteristics such as bearing capacity,settlement and pile axial force,and study the working performance of the extruded support disc group pile under vertical load.In addition,the influence of the pile spacing and bearing plate spacing on the settlement of the pile tops of the group of piles is studied.(2)A new staggered arrangement method is adopted for the squeezed branch pile group,in order to optimize the settlement of the pile group.By contrastively analyzing the squeezed branch pile group which under the flat plate arrangement and the refined squeezed branch pile group,the effect on the vertical load is studied.It also considers the influence of two influencing factors,the spacing between the staggered discs and the pile spacing,which provides reference values for actual project.(3)A new method for optimizing the vertical rigidity of pile groups with squeezed branches and plates is proposed,without changing the pile length,pile diameter and pile spacing,only the number of bearing plates at each foundation pile is changed,so that the stress on the top of the foundation pile is evened.Under the control of genetic algorithm,the optimal arrangement of pile groups is obtained to reduce the uneven settlement difference of the pile group foundation.An engineering example is used to verify the rationality of the method.(4)The secondary development of ABAQUS finite element software establishes a parametric modeling platform for group piles of squeezed and expanded support discs,combines parametric modeling of group pile foundations with pile foundation optimization,realizes automatic modeling and optimization of group piles of squeezed and expanded support discs,improves the efficiency of using finite element software,and significantly reduces the time required for model establishment and optimization. |
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