Research On The Carrying Characteristics Of The Extra-Long And Large Diameter Pipe Pile Based On The Construction Effect

Prestress High Concrete(PHC pipe pile)has the advantages of high strength,low cost,pile quality control,good bearing performance,widely used in the construction of building foundation,highway subgrade and bridge pile foundation.However,the existence of pipe pile construction effect is easy to lead to the deviation of adjacent pile body,resulting in the surface cracking,deviation and structural damage of adjacent structures(structures),especially for the construction of ultra-long and ultra-diameter pipe piles,which greatly limits the popularization and application of pipe piles.In order to study the influence of large-diameter pipe pile construction effect on vertical bearing characteristics of pipe pile,this thesis adopts the method of combining laboratory test,numerical simulation and field test to study the development law of soil squeezing effect of pipe pile during pile sinking and the variation trend of deflection form and bearing performance of pipe pile subjected to construction effect.The main research contents and conclusions are as follows:(1)In the depth range of 4 times the pile diameter spacing of 20 m,the horizontal displacement of soil caused by large-diameter long pipe pile is obviously changed;Besides,the horizontal displacement of soil tends to be flat due to the increase of overlying pressure.The effective range of soil squeezing effect of pipe pile is 10 times of pile diameter.Beyond this range,the horizontal displacement of soil is ignored.The change of pore water pressure caused by pipe pile construction decreases rapidly with the increase of construction distance within the range of 4 times pile diameter,and its external change range tends to be gentle.(1)In the depth range of 4 times 20 m pile diameter spacing,the horizontal displacement of soil caused by large diameter long pipe pile is obvious.Besides,the horizontal displacement of soil tends to be flat due to the increase of overlying pressure.The effective range of soil squeezing effect of pipe pile is 10 times of pile diameter.Beyond this range,the horizontal displacement of soil is ignored.The change of pore water pressure caused by pipe pile construction decreases rapidly with the increase of construction distance within the range of 4times pile diameter,and its external change range tends to be gentle.(2)In the early stage of pile sinking,the soil at the bottom of the pile moves downward and inward to the pipe pile,and the soil at the side of the pile rises upward to form an soil arch at one time of the pile diameter;In the late period of pile driving,the soil at the bottom of the pile is mainly squeezed and dispersed to both sides due to the influence of the soil plug formed by the soil in the pile,and the arch height of the surface soil continues to increase,but the variation range decreases.The maximum horizontal displacement of pile side soil occurs about1/4 pile away from the surface,and the decreasing range of pile side soil displacement is larger within 2-4 times pile diameter spacing.The development trend of soil squeezing effect produced by pipe pile with different diameters is roughly the same.The large diameter and long pipe pile has obvious disturbance to pile side soil and the change range of soil horizontal displacement is large.In addition,the soil properties have a great influence on the soil squeezing effect of pipe pile.The smaller the soil compactness is and the larger the particle size is,the more obvious the soil squeezing effect of pipe pile is.(3)The pile diameter,friction coefficient and pile length of pipe pile have certain influence on the development law of soil squeezing effect.When the height of soil plug inside the pile is roughly the same,the larger the pile diameter,the larger the friction coefficient of pile side,the longer the pile length,the stronger the influence range and effect of soil squeezing effect.Through double pile sinking,it is found that within 4 times pile diameter spacing,both pile top and pile bottom deflect to the side away from the back penetrating pile under the effect of soil squeezing,and the deflection of pile top is greater than that of pile bottom.When the pile diameter is greater than 4 times,only the tip of the adjacent pile deflects away from the side of the rear penetrating pile,and the tip deflection decreases obviously.In addition,it is found that the vertical ultimate bearing capacity of pipe pile decreases after the deflection.The larger the deflection range of pipe pile,the more obvious the decline of vertical bearing performance.(4)Combined with the numerical simulation results,the calculation formula of vertical ultimate bearing capacity of pipe pile was derived by theoretical analysis.Then,combined with the specific deflection form of pipe pile,the calculation formula of vertical ultimate bearing capacity of super-large and ultra-long diameter pipe pile in the Yellow River area under the influence of construction effect was modified,and the reduction coefficient of the calculation formula of vertical ultimate bearing capacity of super-large and ultra-long pipe pile after deflection was proposed.The revised formula is verified by a calculation example.The revised formula can calculate the vertical ultimate bearing capacity of super-large and ultra-long offset pipe pile more accurately.