Research On Evolution Law And Control Measures Of Ground Settlement In Shield Tunneling

With the development of Chine's economy and the expansion of urban areas,city dwellers are confronted with the problems brought by traffic congestion.As metro has played an important role in relieving the traffic pressure,what is crucial in metro construction is tunneling,in the process of which inevitably destabilizes the surrounding soil,changes the conditions of formation stress,causing maldistribution of the stress and the problem of ground settlement as a result.If the settlement is overdone,neither the tunneling could go on wheels,nor the surrounding constructions,roads,underground utilities would be free from destruction.There are numerous methods of tunneling,such as new austrian tunneling,mining tunneling,cut and cover tunneling,shallow tunneling,and shield tunneling,etc.,with the last one typically adopted in urban metro construction.Compared to other methods,shield tunneling has many merits: apart from a speedy drilling,it is non-disruptive to transportation and facilities and immune to season and climate change.It also has technical and economic advantages of constructing long tunnels in deep soft stratum.How to predict and control the ground settlement in shield tunneling have been a major concern in shield construction.Based on the construction of Panhong Section on No.2Metro Extension Line,this paper probes into the evolution law of ground settlement through the analysis on monitoring data of the settlement,conducting numerical simulation analysis by finite element software PLAXIS 3D,comparing the settlement simulation result with the on-site monitoring data so as to provide basis for mastering the evolution law of ground settlement and offer references to settlement control.The main contents of this paper are as follows:(1)Analyzing the mechanical and geometric effect caused by shield tunneling based on the principle of shield tunneling and the mechanism of ground settlement.Comparing and studying the common methods of forecasting shield tunneling,such as experiencedformula method,analytic method,theoretical analysis method,numerical analysis method,etc.with on-site settlement results so as to summarize the settlement law.(2)Mapping out on-site monitoring and measuring point layout on the basis of Panhong construction section on No.2 Metro Extension Line,studying the settlement law of the ground above the axis when the shield passing through different sections and the settlement law of different cross sections by collecting and conducting statistical analysis for settlement data.(3)Setting boundary conditions and mesh generations to simulate the settlement caused by shield tunneling by using the numerical analysis software PLAXIS 3D,comparing the on-site monitoring results with the results calculated by the software,the combination of which could justify the accuracy of numerical simulation and provide reference for settlement control.(4)Studying the major control methods for shield settlement,such as the soil pressure balance method,synchronous grouting and secondary grouting control method,lining segment assembling control method,advance rate control method,direction control method,etc.and comparing both the strength and weakness of them so as to provide settlement control methods.