Study On The Influence Of Surface Loading On The Stress Characteristics Of Existing Bridge Pile Foundations

In recent years,with the continuous encryption and expansion of the Chinese railway network,more and more railway lines need to pass through areas where human activities are frequent,and there are lines where roads and railways cross each other.In the vicinity of the railway bridge pile foundation,there will inevitably be static loads of buildings and piles,as well as vehicle dynamic loads.The presence of these loads will adversely affect the bridge pile foundation,causing the pile foundation to sink and tilt.When the situation is serious,it will affect the safety of trains.Therefore,it is of great practical engineering significance to carry out research on the influence of surface loading on the stress characteristics of existing bridge pile foundations.This paper relies on the lateral pile-loading project of the pile foundation of the Zheng-Xu high-speed railway bridge.Through the establishment of the finite element model of pile-soil interaction,this paper analyzes the stress characteristics of the pile foundation under surcharge load.The main research contents and results as can be seen in the following paragraphs:(1)The research status of pile side loading at home and abroad is analyzed,and the problems and difficulties in pile foundation research are presented.The mechanism of load transfer mechanism,side resistance and end resistance of pile foundation is analyzed theoretically,which provides theoretical support for model establishment.(2)The ABAQUS finite element software was used to study the influence of pile side loading on the bearing characteristics of pile foundation.The results show: For a single pile,stacking reduces bearing capacity of pile foundation,the stress on the front side and the rear side of the pile is obviously different near the pile top.Below the pile depth of 28 meters,the stress on the front and rear sides of the pile are basically equal.The negative skin friction on the front side is greater than the rear side of the pile.The settlement of the pile near the top of the pile and the surrounding soil is greater than the end.On the ground,the settlement of the soil around the pile is larger than the pile top.As the depth of the pile increases,the settlement of the soil and pile tends to be the same.For group piles,the load is mainly carried by the corner pile and the side pile,the load shared by the center pile is the smallest,and the axial force decreases along the buried depth: Corner pile > side pile > center pile.The distribution of the lateral skin friction of each pile parallel to the piles is consistent.The vertical settlement of each pile is basically the same,and the vertical settlement is the largest at the top of the pile and gradually decreases along the depth.(3)The control variable method was used to study the effects of different surcharge distances,surcharge grades and surcharge widths on axial forces,side skin friction,vertical settlement of pile.For single piles,focus on mechanism analysis and analyze the effects of different surcharge distances,surcharge grades and surcharge widths on the mechanical behavior of single pile.For group piles,considering the pile group effect,the effects of different surcharge distances,surcharge heights and surcharge widths on the stress characteristics of each pile are analyzed.(4)The vertical settlement of the surrounding soil and the spatial distribution of the neutral point on the pile side are analyzed,and the spatial distribution of the neutral plane is described.By summarizing the distribution law of negative skin friction,the distribution form of negative skin friction under steady state is simplified,and trapezoidal fitting is used to derive the trapezoidal distribution function of negative skin friction along pile length.The rationality of the trapezoidal model is verified by field measured data.The results show that the error of the pull-down load calculated by the trapezoidal model is less than 15%,which indicates the rationality of the trapezoidal model.