Prediction And Analysis Of Influence On Stratum Settlement Of Subway Shield Tunnel Construction With Synchronous Grouting

In shield tunneling, the shield tail interspace between segments and surrounding soils cancause strata turbulence and ground settlements. Synchronized grouting technology can reducethe deformation of stratum during shield construction. The effect of Synchronized grouting ondeformation amount of soil layer is crucial. To receive good results of grounting, the suitablegrouting parameters is needed. It is necessary to analyse the ground deformation underdifferent grouting parameters and provide reference for selecting grouting parameters inengineering.The FLAC3D which is three-dimensional finite-difference software is used to establish thenumerical model to simulate and analyze shield construction process combined with a line oftianjin subway shield excavation engineering practice. Settlement curves varied along withtime of monitoring points are obtained by simulation and have a good agreement with resultsof practice test.Based on the simulation, this paper researches the discipline of surface movementsinduced by shield tunnel construction, analyses some factors affect surface settlement such asthe grouting pressure, grouting time and the settlement regularity under different soilproperties such as the elastic modulus, internal friction angle and cohesiveness of soil. Theanalysis shows that: when the diffusion processes of slurry is simulated by non-uniformdistribution grouting form considering the gravity,the settlement curves get the best matchwith the practice; the maximum uplift and subsidence value of soil appear in the grouting areaof tunnel backwall; the decrease of surface subsidence caused by the increase of groutingpressure is unconspicuous after the grouting pressure is more than0.2MPa; in cases ofgrouting not timely, surface subsidence bigger and longer; within a certain range increasegrouting quantity can significantly reduce surface subsidence; after soil elastic modulusincreases to a certain value, it’s function to decrease the surface subsidence value becomemore and more unconspicuous; after soil Angle of internal friction increases to24, it’sfunction to decrease surface subsidence value almost can be ignored; the decrease of surfacesubsidence value caused by the increase of soil cohesive force is not significantcomparatively.Preliminary study on the deformation of foundation pit above shield during shieldexcavation and compare the bottom ground settlement under different grouting pressuresshowed that: the sink and upheaval will appear at the bottom of foundation pit due to theshield excavation under, overall the settlement on two sides of foundation pit bottom alongthe tunnel axis is relatively apparent; the sidewall around foundation pit all have the trend totilt into the pit, and the tilt amplitude of sidewall vertical to the tunnel axis is more obvious;the larger grouting pressure can make the foundation pit bottom uplift, and the settlement ofthe foundation pit bottom is more apparent with the smaller grouting pressure.