Study On Deformation Mechanism And Risk Control Of Shield Tunneling Pipeline In Sand

In view of the strong fluidity and dispersion of the sand,it is necessary to study the influence of the shield construction of the sand layer on the deformation of the pipeline.Through theoretical calculations,model experiments and numerical simulation studies,the displacement transmission law of the surrounding soil body and the response mechanism of the stress and deformation of the pipeline are obtained;the shield tunneling parameters of the tunnel construction and the pipeline reinforcement measures are studied.The influence law of structural deformation,the key technology for prevention and control of pipeline disaster induced by new subway tunnel construction is proposed.The main conclusions are as follows:(1)Time sequence analysis of settlement: when the distance from the excavation surface is about(2.5 to 1.0)D,the impact of shield excavation is very small,and the distance from the excavation surface is about(1to-1)D,and it begins to decline significantly.becoming steady.(2)Different pipe-tunnel spacing:As the tunnel burial depth increases,the maximum settlement value of the surface,pipeline and the maximum bending moment value of the pipeline decrease,but the coefficient of the settlement tank width increases instead.Different soil quality:In silty clay than in sand,the surface settlement value and the vertical settlement value of the soil at the depth of the pipeline are reduced,and the impact range caused by construction remains unchanged.The maximum positive bending moment of pipelines in silty clay is reduced compared to sand.Pipeline stiffness: the final vertical deformation of the pipeline is relatively small when the pipeline rigidity is relatively large,and the pipeline vertical deformation curve is relatively gentle when the pipeline rigidity is relatively large.Has little effect.(3)Shield tunneling state:the smaller the speed of the screw dumper,the greater the pressure of the earth bin,the smaller the settlement of the pipeline.When the pressure of the earth bin increases to the equilibrium state,the pipeline bulges.The speed of the screw dumper has little effect on the position of the reverse bending point of the vertical deformation curve of the pipeline.As the diameter of the shield increases,the surface settlement value and the vertical settlement value of the soil at the depth of the pipeline increase,and the impact range caused by the construction is basically unchanged.(4)Soil pressure at the bottom of the pipe: When the speed of the screw dumperis 600 r / min,a certain degree of pipe-soil separation occurs in the pipeline;at 500 r /min,the degree of pipe-soil separation is small,and the 400 r / min shield machine has an upward bulging effect.Finally,the reinforcement measures of pipeline are simulated,and the reinforcement effects of different measures and different parameters of the same measures are summarized: within a certain reasonable range,with the increase of grouting thickness around the pipeline and the increase of grouting layer modulus;the increase of tunneling pressure of shield;the increase of grouting layer strength of shield tail;the increase of thrust of shield jack;the increase of pipeline settlement value and the decrease of maximum stress value.