Study On The Additional Effect Of New High-Speed Subgrade On Adjacent Existing Subgrade

With the vigorous development of China's railway construction,more and more new railway lines have been built adjacent to existing railway lines.The construction and operation of new lines has more or less disturbed the existing railway lines,and affected the safety of existing lines.Scholars have begun to pay attention to the study of such engineering problems.There are few related engineering cases,and most of the research focuses on field monitoring?numerical calculation of additional settlement,treatment of combined disease and uneven settlement of existing lines,field construction methods.There is a lack of systematic research on the theory of additional settlement of existing lines.This paper relies on the project of “Lunan Expressway Introducing Beijing-Shanghai High-speed Railway Qufu East Station Project”,and uses theoretical calculations and numerical calculation methods to study the additional influence law of new lines on adjacent existing lines,introduces the calculation method of additional settlement theory,and by means of the calculation results to perform construction treatment for projects that do not meet the conditions of settlement under existing lines.These provide a certain theoretical reference and the construction reference for the similar project.Through analysis and research,the following main conclusions are obtained:(1)When the distance between the new and old lines is relatively close,the new line has a greater impact on the existing line.As the distance increases,the additional influence decreases.In this paper,when the distance between the new and old lines exceeds 22.9m,the additional influence which is less than 1mm can be ignored.(2)In the section of new and old lines connected,the new roadbed is partially filled at the slope of existing lines.Therefore,the base stress distribution is different from the traditional single roadbed.The research of the base stress distribution is carried out by numerical calculation software,the results show that the new line of the connected road section will produce the base stress diffusion on the foundation surface.In the model used in this paper,the diffusion range of combined section extends to the center of the section of the old roadbed.And the writer proposes a reference formula for such base stress.(3)Numerical calculation and theoretical calculation of foundation settlement after filling the new line,can accurately reflect the settlement law of the foundation.The calculation results show that the foundation settlement of the new line filling area is the largest in the crosssection of the subgrade;The additional settlement of the existing line at the junction is too large without treatment,the settlement requirements are not met and engineering treatment must be carried out;After reasonable engineering treatment measures,the settlement of the existing line can be controlled within reasonable requirements.(4)The most effective way to improve the additional settlement of existing lines is to reduce the weight of roadbed filling.In project,it can be realized by adopting new lightweight roadbed packing.In this paper,lightweight concrete is used to fill the roadbed,and the settlement of existing lines is reduced more than 2 times.(5)Using Pile-slab structure to foundation reinforcement can not only significantly improve the settlement of the foundation,but also minimize the construction disturbance to the existing line.It can be used in projects with high disturbance requirements.(6)There is a slight difference between the theoretical calculation results and the numerical calculation results,which are related to the two algorithms with different calculation methods.However,the settlement laws and values calculated by the two are basically in line with experience,which can provide reference for settlement prediction in actual engineering.It can be used as a safety assessment method before construction.