Research On The Law Of Ground Surface Settlement When Shield Tunneling Passes Through The Soil Reinforced Area At The End

In recent years,as the above-ground space has become more and more crowded,and people's demand for faster travel has increased,this has led to unprecedented development and utilization of underground space.The shield construction method has become the main construction method of urban subway tunnels due to its many advantages,such as high degree of automation,fast excavation speed,and little influence from natural conditions.But at the same time,shield construction also brings many environmental and safety issues.Among them,the initial excavation stage of the shield is the key link of the shield construction,and it is the accident-prone stage during the shield construction process.It should be the focus of research..However,the current research on shield tunneling mainly focuses on the effect of shield tunneling on surface settlement or soil layered settlement during the normal tunneling stage,and there is little research on shield starting section.Therefore,it is particularly important to study the surface subsidence during the initial stage of shield tunneling.Based on the initial construction project of the shield tunnel at Aofeng Road Station of Fuzhou Metro Line 4,this paper uses theoretical analysis and numerical simulation to analyze the ground settlement laws caused by the shield tunnel at the beginning of the stage when it passes through the soil reinforcement area at the end.Research,the main research work and results are as follows:(1)Through literature reading and related investigations,we discussed and summarized the key technologies,points and key issues that need to be paid attention to in the initial excavation process of shield tunnels,and summarized the specific methods and measures of each technical link.(2)Taking the shield tunneling project of Aofeng Road Station as an engineering example,using elastic thin plate theory,soil slipping instability theory,soil disturbance limit equilibrium theory and related knowledge of loose circle,establish the corresponding mechanical calculation model,The reinforcement range of the soil at the end of Aofeng Road Station is obtained,that is,the longitudinal reinforcement length t=12.87 m,the transverse reinforcement length B=1.37 m,and the vertical reinforcement length H1=H2=1.55 m,which is slightly smaller than the general experience value.This result not only provides a theoretical basis for determining the soil reinforcement range at the end of Aofeng Road Station,but also provides a theoretical reference for the subsequent numerical simulation study of shield tunneling.(3)Through the research on the mechanism of ground settlement caused by shield tunneling,the factors and main reasons of the ground settlement caused by shield tunneling were analyzed and summarized.And according to the characteristics of the ground subsidence caused by the shield tunneling,the Peck formula is used to fit and analyze the measured data of the ground subsidence of the shield tunneling project at Aofeng Road Station.The value range of the obtained formation loss rate V is V=0.5? 1.3%,the value range of settlement trough width i is i=6?7m,which is basically the same as that of general soft soil areas.By comparing the actual measurement results and prediction curves of several sections,the results obtained are relatively consistent,which fully shows that the characteristics of the surface subsidence caused by the shield initiation are consistent with the Peck settlement law.(4)Using the large-scale finite element numerical simulation software Midas/GTS NX,first analyze the displacement field and stress field of the soil in the reinforcement zone at the most unfavorable stage of the opening of the shield tunnel door removal,and then study the shield tunneling The surface settlement caused by the initial reinforcement zone.According to its settlement characteristics,with the boundary between the soil reinforcement area and the non-reinforcement area at the end of the shield,the development of the surface settlement caused when the shield passes through the initial reinforcement area is divided into five stages.The analysis shows that the settlement rate caused by the tail of the shield machine passing through the interface is the fastest,which indicates that this stage is the most dangerous stage for the start of the shield.According to the research results,effective control measures are proposed to provide a theoretical basis for the safe launch of the shield.