| By the end of December 2018,37 metro operation cities had been opened in China,with operating mileage reaching 5697 kilometers,45 metro cities under construction and 5520.8kilometers under construction.With the advancement of rail transit construction,the overlapping line method can solve the problems of line network transfer,narrow road,avoiding bridge pile foundation and reducing house demolition.However,the study of overlapping shield tunnels has obvious lag compared with engineering practice,and the guidance for engineering construction is insufficient.Therefore,it is necessary and urgent to strengthen the study of overlapping shield tunnels.Based on the overlapping shield tunnels between Hongling North Station,Shougang Station and Honghu Station of Shenzhen Metro Line 7,this paper adopts the methods of numerical simulation,field test and monitoring measurement to solve the key technical problems in the construction of overlapping shield tunnels in Metro sections.The main research contents and results are as follows:1.Based on the analysis of surface settlement,segment lining displacement and segment internal force variation law caused by different construction sequence of overlapping shield tunnels,the division criteria of construction sequence of overlapping shield tunnels and the control criteria of displacement and internal force of pre-built tunnels caused by post-built tunnels are established by using finite element numerical simulation method.2.Through numerical simulation of conventional shield tunnels and overlapping shield tunnels,the influence of self-weight of shield tunnels and construction load on the lining of downline segments is analyzed,and the special design of lining segments of overlapping shield tunnels is established.3.Based on the research results of Chapter 2 and the previous construction experience,it is concluded that the overlapping shield tunnel should adopt the following working procedures.The influencing factors of the overlapping shield tunnel construction are analyzed,and the key technology of the overlapping shield tunnel construction is established.4.Through numerical simulation and field test of two kinds of sandwich soil(unconsolidated soil and reinforced soil)in the process of "first up and then down" of overlapping line tunnel,the differences of surface settlement,segment displacement and segment internal force caused by two kinds of sandwich soil conditions are analyzed,and the strengthening technology of intermediate sandwich soil in overlapping line shield tunnel is established.5.Taking Hongling North Railway Station to Shaogang Railway Station as thebackground,through the comparative analysis of numerical simulation,PECK formula and on-site monitoring,the environmental impact factors of overlapping shield tunnel construction on the surrounding environment are obtained,and the control countermeasures of overlapping shield tunnel construction on the surrounding environment are formulated. |
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