| Based on the previous study of shield tunnel floating problem, furtherinvestigation is carried out theoretically and numerically. Some useful conclusions aredrawn, which may be helpful in the design and construction of cross-river tunnel. Themain work is summarized as follows:Firstly, the research status of tunnel anti-floating study is presented. Themechanism of tunnel floating, the anti-floating effect of segments and overling soil,and the computing method of smallest covering depth are provided. Based on thetheoretical analysis of equilibrium states of excavation face and shield segments awayfrom shield tail, formulas to calculate the smallest covering depth which satisfys theanti-floating requirements are derivedSecondly, based on the existing uniform ground movement model of shieldtunnel, a new model considering the grouting buoyancy is established, and then thecorresponding deformation formulas of soil in the elastic half-infinite plane isobtained by virtue of Melan equation. The two-dimensional solution to soildeformation considering the floating of serous fluid is finally determined throughsuperposition of the above mentioned deformation and the settlement caused byground loss.Thirdly, combined the Fuhe bridge project which is the sub-project of No.1Nanchang metro with the finite element software ABAQUS, the lining segment andthe surrounding soil are investigated. The deformation of the surface and deep soilsubjected to segment floating is discussed in detail. Through displacement analysis ofthe surface and deep soil, the soil-compacting effects due to the floating of segment isobtained. Comprasion study is performed among the results of numerical simulation,the smallest covering depth formulas and the two-dimensional analytical formulas ofsoil deformation, and it is found that one matches well with the other.Lastly, the surface deformation at different overlying soil thickness, soil propertyand grouting material property are computed and the corresponding deformation lawsconsidering serous buoyancy are obtained, from which some practical suggestions tocontrol the deformation of river bottom are provided. |
