Study On The Influence Of Stacked Tunnel Excavation On The Surface In Complex Environment

With the continuous development of China’s subway traffic construction,the subway construction conditions are more and more limited,especially in the shield tunnel construction of the old urban area,which often encounter very complex underground environment.For example,the underground pipeline structure and the surrounding soil mass have reached the balance state of displacement field and stress field,and the stratum loss caused by shield construction will often cause the surface soil layer production The displacement,especially under the multiple disturbance of the overlying tunnel,is very complex,which affects the normal use of the pipeline and endangers the safety and interests of urban life.According to the construction characteristics of the shield tunnel,based on the complex function theory,this paper studies the law of deformation and stress change of the shield tunnel.In addition,a three-dimensional finite element model is established to study the influence of the shield tunnel excavation on the deformation of the surface soil under the complex environment.The main research contents are as follows:(1)Based on the case study of the tunnel construction in Zhengzhou metro,the monitoring results of surface settlement,gas pipeline settlement and additional stress of the segment in advance of the stacking line are analyzed,and the characteristics of the construction of the complex stacking line tunnel are summarized.(2)By using complex function theory and Schwarz Alternating method,an analytic algorithm of displacement of laminated tunnel in semi infinite elastic plane is put forward.The solution process is successfully realized by computer programming.The surface deformation and displacement around the tunnel during excavation of laminated tunnel in semi infinite elastic plane are obtained,and the influence of superposition of single tunnel in laminated tunnel is analyzed,which is verified by finite element calculation.On this basis,considering the design factors during the construction of the shield,such as:different buried depth of the shield and different spacing of the shield,the variation law of the surface soil layer under the influence of single factor is obtained.(3)Based on the finite element software and reasonable constitutive model,a refined three-dimensional calculation model of Zhengzhou Metro’s laminated line project is established,focusing on the analysis of the impact of the construction and excavation of the laminated shield tunnel in complex environment.The calculation of the vertical settlement of the pipeline along the direction of excavation is consistent with the field monitoring results.After the rationality of the numerical simulation method is verified,and the construction environment of the laminated shield is further analyzed Analysis of pipeline deformation and safety.(4)Through the finite element method,considering the design and construction factors during the excavation of the laminated shield tunnel,such as:different excavation sequence of the laminated shield,filling of the construction mud control effect,shield top thrust and grouting pressure,the change rule of single factor construction control on the surface soil layer is analyzed.(5)Based on the example of Zhengzhou Metro stacked line section project,combined with complex function theory,numerical simulation method and construction site monitoring data,this paper analyzes the deformation disturbance of the overlaying soil layer of the stacked line tunnel,summarizes the deformation control measures,and provides theoretical guidance for the design and construction process of the stacked line tunnel.