The Numerical Simulation Study On Static Pressure Variable Section Pipe Pile Bearing Mechanism And Squeezing Effect In Red Clay Geology

The bedrock in the karst area is undulating and the overburden soil is mostly red clay.Red clay is a regional special soil,mainly distributed in Guizhou,Yunnan and Guangxi.The red clay has the characteristics of being hard and soft,and the upper layer of soil near the surface is mostly hard or hard plastic,and the soil under it is mostly plastic or softplastic.The natural water content and fracture of hard or hard plastic red clay is smaller than that of plastic and soft plastic red clay,and the physical and mechanical properties of red clay are stronger than that of red clay in the upper hard state or hard plastic layer state.PHC pipe pile is a kind of concrete prefabricated structure with high strength made byprestressed pretensioning method and rotary centrifugal forming method.This type of pile has higher bearing capacity,simple construction and low cost,and has become a common form of pile foundation for high-rise buildings.Under the action of pile top load,PHCpipe piles will gradually reduce the axial force along the depth from top to bottom.According to the characteristics of this type of force,the pile type is optimized,and the equal section pipe piles are evolved into large pile diameters.Small variable section pipe piles to save material.Because the vertical bearing capacity of the variable section pipe pile is composed of pile side frictional resistance and pile end resistance,and supporting force of the soil at the variable cross section,variable cross-section pipe piles are used in the red clay foundation,and the variable cross-section is set at high strength.On the hard plastic soil layer,the hard clay-soft property of the red clay can be utilized to exert the bearing capacity of the hard plastic soil layer.This paper uses the FLAC^3D software to simulate the static pressure variablecross-section pipe pile on the red clay under the geological conditions of a certain red clay in Liuzhou.The deformation and bearing characteristics and the soil compaction effect are explored.The main work and research results of this paper are given.as follows:（1）The FLAC^3D software is used to numerically simulate the static load test of the PHC pipe pile of the same section and compared with the actual static load test results to select a parameter model for numerical simulation that is basically in line with the actual situation of the engineering pile and soil.the amount.Based on this,the optimization of pile type is carried out,and a numerical simulation model of variable section piles isestablished to find the optimal variable section ratio and the optimal variable section position of the variable section pipe piles,and the stress field and deformation field of piled soil are analyzed.Research indicates,the maximum stress of piles of equal section piles occurs at the top of piles,and the maximum stress of piles of variable section piles occurs at variable sections.The difference in axial force distribution and pile frictionresistance distribution between variable section piles and equal section piles is that there is a sudden change in the variable section of the variable section piles.In addition to thesudden changes at the variable section,the distribution curves are roughly equal.Section piles are similar.From the data of the axial force analysis chart,it can be seen that variable section piles with a ratio change ratio of 0.6 cannot meet the design requirements,andvariable section piles with a ratio change ratio of 0.8 meet the design requirements.Under the maximum load of 4000KN,the variable cross-section is set at 1/4 of the depth of the pile,which can give full play to the characteristics of hard and soft under the red clay.From the economical point of view,the ratio of the ratio of the pile to the material of the variable cross-section is 0.8 The 500mm equal-section pipe pile with pile diameter and other variable cross-section piles satisfying the design requirements are saved.Compared with the 400mm equal-section pipe pile with pile diameter,the settlement of the pile body is reduced and the pile is optimized.（2）In the background of the actual pipe pile engineering where the bearing capacity does not meet the design requirements due to the squeezing effect,FLAC^3D software is used to numerically analyze the soil deformation field of the equal-section pipe pile and the variable-section pipe pile in the group pile environment.Compare the squeezing effect of the two types of piles.Research indicates,in the case of the same pile center distance,when the pile sinks to the same depth,the horizontal displacement of the soil of thevariable section pile is smaller than the horizontal displacement of the soil of the equalsection pile.The surface bulge of the variable section pile is smaller than that of the equal section pile,indicating the variable section pile.The effect of squeezing soil is smallerthan that of equal section piles.