Research On Influence Of Synchronous Grouting Pressure On Segment Lining Floating During Shield Construction

The segment up-floating during the construction of shield tunnels is very unfavorable to the operation and maintenance of the tunnel,and is likely to cause safety hazards.Taking a shield tunnel project in Guangzhou Metro as the background,this paper obtained the filling and diffusion law of slurry in the shield tail gap and stratum fissure under different grouting pressure by means of theoretical calculation and numerical simulation.Considering the floating volume of the segment ring and the formation’s and segment’s stress state as well as various aging parameters of slurry,a refined three dimensional load-structure model of the segment rings subject to floating load is established based on the optimized formation resistance coefficient and the transverse stiffness efficiency of the segmental lining.Subsequently,the stress characteristics of the segment and bolt under floating load are discussed.The main contents are as follows:(1)Three grouting methods commonly used in shield tunnel were introduced briefly and the diffusion process of slurry injected into shield tail was expounded.Based on the mechanism of segment up-floating,the generation and components of shield tail gap are explained,and eight reasons for segment floating are summarized.According to the characteristics of buoyancy load,the buoyancy load can be divided into static buoyancy and dynamic buoyancy.(2)From the perspective of synchronous grouting,the simulation of fracture development in actual condition is realized by introducing random fractures.The unidirectional coupling calculation of two physical interfaces,slurry filling diffusion field and seepage field namely,is carried out in the calculation domain.The circumferential slurry filling pressure of the segment was extracted and compared with the theoretical results,which verified the reliability of the numerical model.Finally,based on the numerical model and setting different grouting pressure,the filling and diffusion law of slurry in 300 s after grouting into shield tail is studied,and the influence of grouting on formation seepage field is further analyzed.(3)Considering the time effect of grouting,the dissipation of grouting pressure,deformation modulus of slurry,permeability coefficient and dynamic viscosity of grouting variation with time were taken into account in the calculation model,then the characteristics of displacement and stress of stratum and segment related with time effect of grouting are analyzed.(4)Based on the principle of stiffness equivalence,the deformation modulus of strata in Muir Wood theory was modified,in which not only the time-dependent function of slurry elastic modulus was introduced,but the uneven distribution of slurry filling layer and segment integral floating in grouting layer are considered,then the equivalent resistance coefficient distribution of strata in the polar coordinates at different grouting time are obtained.By evaluating the equivalence of the transverse bending performance of the modified homogeneous ring and the assembled segment ring,the relationship between the effective rate of the transverse stiffness and the bending stiffness of the joint is deduced.Finally,the calculation method of the bending stiffness of the joint is deduced based on the theory of the suitable reinforcement failure of the single reinforcement section.(5)The optimized ground resistance coefficient and lateral bending stiffness efficiency are introduced,and the refined three-dimensional load-structure model is established based on the actual engineering parameters.Based on the model,the displacement and stress characteristics of segment and bolt in different construction stages and longitudinal vertical curve of shield tunnel under floating load are analyzed.