Study On Foundation Deformation Of Abutment By Pile Foundation Underpinning Of Urban Overpass

Under the great situation of rapid urbanization,underground transportation has also developed rapidly and has gradually become an indispensable transportation mode for large and medium-sized cities.In the subway route planning,the shield construction cannot be completely avoided directly crossing the existing building structure,and the most common form is the pile foundation crossing the existing structure.In this regard,the commonly used means is pile foundation underpinning.Most of the underpinning structure of the underpinning project still needs to be used normally during the construction of the underpinning.Therefore,the stability of the structure is very high in the design and construction of the underpinning.If large deformation occurs,serious economic losses will result.And social influence.Therefore,the prospective study of the actual project of pile foundation underpinning,analysis of its settlement law and the key locations affected by it can effectively prevent the damage caused by the underpinning construction.This paper relies on the abutment pile foundation underpinning of the F-channel of the Huanghe Road overpass in Zhengzhou City.Based on the design data of the underpinning,the paper analyzes the difficult and difficult points in the process of the underpinning and the locations that may be affected.Using ABAQUS finite element software,the 3D solid model of the active underpinning structure is established and finite element analysis is carried out.The settlement law of the influence of the active underpinning process on the new and old foundation of the abutment is obtained by numerical simulation,and compared with the on-site monitoring data.The results show:(1)In the preparation stage of pile foundation replacement,the new pile is pre-stressed to cause settlement.The purpose of this process can eliminate the early settlement and make the replacement more stable.The replacement process is jacked up by the jacking method.From the result,It has good control over structural stability.(2)During the staged loading stage of the jack,the abutment is subjected to vertical upward displacement from the bottom load of the bottom and has a downward upward displacement and a concave;the axial force of the supporting pile gradually approaches 0 with the loading of the jack,which is subjected to the upper structure.All the transmitted loads are transferred to the new piles.At this time,it is the most ideal state of intercepting piles;the load-bearing beams are subjected to the load of the jacks to form settlements and form depressions;the replacement piles are settled at this stage and produce compression deformation.(3)The structure is affected by a large position: when the jack is loaded,the abutment and the supporting beam are both concave,and the deformation of the middle part of the bottom surface should be monitored to avoid cracks;the force of the supporting beam in the project is eccentric,and the settlement and stress are biased to a large position.In the vicinity of the pile,the inclination of the pile should be controlled during construction;the position of the maximum stress of the replacement pile is on the inside of the structure of the pile top,and the joint with the support beam is prone to cracks.It is recommended that the structural design should be attached to the reinforcement.Monitoring should be strengthened.(4)Through the comparison between the field measured data and the numerical simulation results,the difference between the two values is small,and the settlement trend of the measuring points is the same,so the modeling is successful.The conclusions obtained in this paper can provide reference for engineering construction and related engineering research.