Study On The Lateral Effect Of High Speed Railway Bridge Substructure Caused By Embankment Undercrossing In Soft Soil Covered Area

Bridges account for a large proportion of high-speed railways in eastern China.In urban and rural construction and highway construction,the number of new embankment under high-speed railway bridges is increasing.The soft soil is widely distributed in the eastern region.The filling of the new embankment will cause the lateral movement of the foundation soil in the bridge site.The bridge pile foundation will be flexed and deformed after being subjected to the lateral pressure of the soil,which will cause the lateral deviation of the pier and abutment,which will have an adverse impact on the driving safety of high-speed trains.Based on the background that planned roads undercross simply supported beam bridges of high-speed railway in soft soil covered area,this thesis analyzes the lateral effect of the substructure of high-speed railway bridge caused by embankment undercrossing.The main research contents are as follows:(1)Midas GTS NX is used to establish a two-dimensional finite element model to analyze the lateral displacement of soil in the bridge site caused by embankment filling.It is found that the lateral displacement increases first and then decreases along the depth distribution curve,and the surface soil of the foundation moves close to the embankment,and the deep soil of the foundation moves away from the embankment.The lateral displacement in the foundation mainly occurs in the soft soil layer,and there is almost no lateral displacement in the underlying hard rock layer.(2)The sensitive parameters of soil lateral displacement in the embankment-soil system are analyzed,and the quintic polynomial is selected to fit the curve of soil lateral displacement along the depth distribution.According to the sensitive parameters such as embankment surcharge grade and embankment filling width,the finite element calculation combination of corresponding groups is designed by three-level Box-Behnken method,and the polynomial curves of soil lateral displacement under each combination are obtained respectively.The explicit relationship between the coefficients of polynomials and sensitive parameters is obtained by regression fitting with response surface method.(3)Midas GTS NX is used to establish a three-dimensional finite element model to analyze the lateral impact of embankment undercrossing on the substructure of high-speed railway bridge.The results show that after embankment filling,the flexural deformation of adjacent pile foundation makes the pier deflect laterally close to the embankment,the upper area of pile body produces large additional bending moment,and the pile body at the junction of soft and hard strata presents large additional shear force and bending moment.The lateral displacement and additional internal force of the substructure of high-speed railway bridge increase with the increase of embankment surcharge grade and surcharge width,and increase with the decrease of soil compression modulus.(4)Considering the friction influence between the superstructure and substructure of the bridge,comparing the calculation results of whether the friction force between pier and beam is applied to the pier top,the results show that the friction between pier and beam will significantly reduce the lateral displacement of the pier top.With the increase of the lateral free displacement of the pier top,the limiting effect of friction on the displacement of the pier gradually decreases,and the lateral displacement of pile foundation is little affected by the friction between pier and beam.(5)A simplified method for calculating the lateral effect of embankment undercrossing on the substructure of high-speed railway bridge is proposed: establish the differential equation of lateral force of passive pile basing on the soil displacement method and Vlasov twoparameter foundation model;regard pile group as a single pile and establish the differential equation of lateral force of equivalant single pilecap-pier.The lateral displacement of soil calculated by response surface fitting formula or two-dimensional finite element model can be input to obtain the lateral deformation of pile foundation and lateral displacement of pier top.With 54 figures,17 tables and 81 references...