Research On The Floating Law And Control Measures Of Shield Tunnel Segments In Ultra-soft Soil Strata

Shield construction is a commonly used scheme in urban subway construction,but it is often faced with the problem of shield tunnel segment floating in the construction process,especially in the construction of soft soil layer,because the surrounding soil strength is low,the segment is very easy to be disturbed by the construction means,resulting in serious floating phenomenon.Excessive floating volume will often lead to a series of diseases such as segment cracking,wrong platform and leakage,which is not a small hidden danger for the safety of tunnel construction and operation.The operation environment faced by the construction of Suzhou rail transit line S1 is a complex stratum with extremely complex deep muddy clay,shallow micro confined water layer and deep confined water layer.Compared with soft soil layers such as Nanjing,Shanghai and Hangzhou,Suzhou muddy soil is more unfavorable to engineering construction in terms of strength,compressibility,permeability and sensitivity.Based on the construction of shield tunnel in Zhanxi section of Suzhou rail transit line S1,this paper studies the floating law of shield tunnel in the super soft soil layer of full section muddy silty clay in Suzhou through literature investigation,on-site monitoring and numerical simulation.Based on the research results of numerical simulation and slurry ratio test,this paper puts forward construction suggestions to control the floating of tunnel.The main research contents and achievements of this paper are as follows:(1)Through the analysis of field monitoring data,the floating law of shield tunnel in muddy silty clay layer during construction period and the influence of construction parameters such as grouting pressure difference,grouting amount and shield tunneling speed on the floating amount of shield tunnel are obtained.(2)A three-dimensional numerical model of shield ring by ring excavation considering slurry hardening process,slurry setting time,slurry density,shield tunneling speed,grouting pressure difference,grouting volume and slurry static buoyancy is established.The results are compared with the field monitoring data to verify the rationality of the model.On this basis,the quantitative effects of the length of non solidified slurry area,grouting pressure difference,grouting filling rate and slurry density on the maximum floating amount of shield tunnel segments during construction are studied,and the relationship between the influence degree of factors is determined,so as to provide construction suggestions for shield construction in this stratum.(3)Through the indoor slurry Proportioning Test,the influence law of the content of each component of the slurry on its physical properties is studied.Combined with the numerical research results,taking the setting time,shear yield strength,density and early strength as the relevant indexes of the slurry anti floating performance,the comprehensive balance method is used to optimize the slurry proportioning design.Finally,some suggestions on slurry ratio for controlling the upward floating of shield tunnel are put forward.