Study On Evaluation Method Of Bearing Capacity Of Abutment Pile Foundation In Collapsible Loess Area Based On Real-time Monitoring

In the pile of bridge design,according to the importance of the structure,the some or all of pile's negative friction resistances are consider when the collapsible loess layer collapses.The negative friction resistance of the pile foundation in the collapsible loess area is caused by the humidification deformation of the loess,which will make the calculation of the negative friction in the pile foundation design is too large,resulting in the safety reserve in the pile foundation too much and produce unnecessary waste.In this paper,based on the influence of the bearing capacity of the pile foundation in the collapsible loess area on the humidification deformation of the loess,the factors affecting the bearing capacity of the loess under the condition of humidification and deformation are analyzed.The main research work in this paper includes:(1)To explore the characteristics of collapsible loess humidification deformation.The causes of humidification deformation in loess are analyzed,including the large pore,structural and water sensitivity characteristics of loess.This paper summarizes the calculation method of humidification deformation of loess,and carries out the lateral compression test of soil with different water content in the Southern mountainous area of NingXia loess,and obtains the relevant parameters of calculating the humidification deformation of the loess by the modulus reduction method.(2)The formation and distribution of negative friction resistance of pile foundation and its influence on pile foundation are analyzed.In order to analyze the negative friction resistance of the pile caused by the humidification deformation of the collapsible loess,and to analyze the influence of the resistance on bearing capacity of pile foundation,FLAC3 D modeling software was used to simulate the humidification deformation of soil by modulus reduction method.In this way,wetting deformation strength,humidification deformation depth and other factors were analyzed.(3)In view of the problem of negative friction resistance caused by humidification of loess,this paper presents a method of bearing capacity evaluation of pile foundation based on load equivalent method.Using the load settlement curve of the single pile,the displacement of the pile caused by the humidification deformation of the pile soil is equivalent to the displacement of the pile caused by the increase of the pile top load,and the negative friction resistance is transformed into the positive friction calculation.Based on the load settlement curve of single pile,the parameters of load transfer model are inversely computed,and the load transfer differential equation is used to solve the axial force and displacement curve of pile under different pile top loads.For the change of humidification water content along the depth,the deformation of the pile side soil with depth is calculated by the secant modulus method,and combined with the displacement curve of the pile under the load of the pile top,the location of the neutral point can obtained,In this way,the method of evaluating the ultimate bearing capacity of pile foundation under the condition of wetting deformation of pile collateral loess is formed,and the strength of pile body is checked according to the negative friction resistance and the position of neutral point.(4)Based on the Ningxia Gushi Expressway,the collapsible loess roadbed monitoring system including the cross-bridge pile foundation was designed and deployed.The simulation analysis of the relying on engineering was carried out by FLAC3 D to simulate the effect of the pile-side soil humidification on the pile foundation.