Study On The Supporting Parameters Of Steel Pipe Crossing Bracing In Subway Station Tunnel

Following the rapid development of metropolitan rail transit construction,the metropolises in China have begun to construct mass rail transit in a large scale.A large number of open excavation and deep excavation are carried out to build subway stations,and the combined form of bored pile and steel pipe has been widely used as an economical and effective foundation pit support.The foundation pit excavation will produce the deformation of the foundation pit,and the development of the deformation will cause the hidden danger and even accidents of the foundation pit.Therefore,in order to control the foundation pit before the accident,the theoretical research,design and construction of the deep foundation pit are very important.The deep foundation pit supporting technology has become difficulty and hotspot.The main structure of the subway station for Chongqing metro Line Four is 22.3m-23.35m wide and the foundation pit is 19.29m-20.81m deep.Based on the subway station,the parameters of steel tube braces for foundation pit are studied in this article.The main research and conclusion are as follows:1.The construction examples and research documents of deep foundation pit,especially the deep foundation pit in domestic and abroad,especially the subway station,are collected,and the characteristics of each project are compared,and the analysis methods of deep foundation pit support are summarized.2.We summarized the geological and hydrological conditions of the subway station at Gangcheng station.The monitoring plan of the project is put forward,and the construction monitoring is completed.The analysis and monitoring results show that the deep foundation pit of Gangcheng station is stable at all stages of construction,and the deformation values of all monitoring items are small.3.The large finite element software MIDAS GTS NX is used to simulate the excavation analysis.The stability calculation of foundation pit is done by using the software of Li Zheng foundation pit and the limit equilibrium method.The displacement,bending moment,shear force and ground settlement of pile under two methods are analyzed,and the calculation results are compared with the monitoring data.The monitoring data and GTS NX analysis were similar.The analysis results of Lizheng foundation greatly.The comparison shows that the foundation pit is stable at all stages of excavation.The design parameters of steel pipe cross braces are too conservative,so it is necessary to compare the parameters of steel tube braces.4.Finite element analysis is used to study the influence of steel braces on the stability of foundation pit.The main parameters of the study are horizontal spacing,vertical spacing and storeys of steel braces,stiffness and prestress of steel braces,pile diameter and pile spacing.For each parameter,several schemes are compared,and the influence of each parameter on the stability of foundation pit is summarized.The conclusion is as follows:the increase of the number of supporting layers can reduce the deformation of the foundation pit and the pile body,reduce the moment value of the pile body,and increase the displacement of the pile body,which can reduce the deformation of the retaining structure.When the prestress reaches a certain value,the effect of the control deformation becomes not.It is obvious that pile diameter and pile spacing have obvious influence on the deformation and internal force of the retaining pile,and the change of support stiffness and horizontal distance has little influence on the deformation and internal force of the retaining pile.5.By using the result of the research on the effect of steel tube braces on the stability of foundation pit,an optimization plan is put forward for the supporting design of this project.The optimum supporting scheme of the foundation pit is determined by comparing and analyzing the transverse distance,vertical spacing,and number of layers,stiffness,prestress,pile diameter,pile spacing and the cost of the project.6.The research result of this article has practical engineering significance and reference value for similar foundation pit support design.