Study On Influence Of Foundation Pit Group Excavation On Deformation Of Adjacent Railway Subgrade And Safety Evaluation

With the continuous advancement of national strategies such as a powerful country in transportation and the Belt and Road Initiative,various transportation engineering construction projects have continued to land,and the excavation of foundation pits near the subgrade of existing railways has gradually increased.Especially for the new line viaduct project,a large number of foundation pits combined with the tight schedule and heavy tasks,inevitably appeared the excavation of the foundation pit group adjacent to the existing railway subgrade.However,the train runs fast and the deformation needs to be strictly controlled.Once the construction measures of the foundation pit groups are improper,it is very easy to cause major engineering accidents.Therefore,it is urgent to carry out research on the deformation evolution of adjacent railway subgrade under the condition of excavation of foundation pit group,and comprehensively evaluate the safety status of railway subgrade to provide reference for engineering decision-making.Based on the Mulanxi Bridge Project in Putian,Fujian Province,this paper comprehensively uses various methods such as literature,field monitoring,and numerical simulation to study the influence of excavation of foundation pits on the deformation of adjacent railway subgrades.The research is based on the on-site monitoring of an independent foundation pit project,using measured data to verify the reliability of the finite element model,and then using a large number of simulation schemes to study the influence of a single foundation pit excavation and a group of foundation pits on the deformation characteristics of adjacent railway subgrades.On this basis,the safety evaluation of railway subgrade under the condition of excavation of foundation pit group is studied.The main research results are as follows:(1)Aiming at the influence of a single foundation pit excavation on the deformation of the subgrade,a series of finite element models are established to study the influence of the excavation depth of the foundation pit,the distance between the foundation pit and the subgrade,and the stiffness of the upper layer of the foundation pit on the deformation law of the railway subgrade.Through the analysis of the finite element calculation results,the evolution of the railway subgrade deformation safety zone is revealed,and the deformation law of the railway subgrade in the longitudinal,horizontal and depth directions is obtained,which lays a solid foundation for subsequent research.(2)The deformation characteristics of railway subgrade under the condition of excavation of foundation pit group are studied.By using 36 different simulation schemes,the influence of three different factors on the deformation of railway subgrade is analyzed,including the number of foundation pits,the distance between foundation pits and subgrade,and the distance between adjacent foundation pits.Firstly,the safety zoning of railway subgrade under the condition of multi factors is studied,and the subgrade deformation areas are divided into three categories: influence area,warning area and danger area;Then,the deformation laws of railway subgrade in longitudinal,transverse and along the depth direction under different influence factors are analyzed.It is found that the number of foundation pits and the distance between foundation pit and subgrade have greater impact on the subgrade deformation among the above three factors.(3)The safety evaluation index system of railway subgrade is established by considering the factors of foundation pit itself,adjacent foundation pit group,engineering geological conditions and railway subgrade conditions;Combined with the research on the influencing factors of foundation pit group,the weight of each evaluation index is determined by using the analytic hierarchy process,and finally the fuzzy comprehensive safety evaluation model of railway subgrade is established,which is applied to the actual project to provide reference for project decision-making.