Study On The Rule And Mechanism Of The Influence Of Metro Shield Synchronous Grouting On Surface Subsidence

As the key processes of shield tunnel construction,the influence law and mechanism of the post grouting can provide reference for the safe and efficient construction of the subway.Instead of comprehensive analysis,most of the existing researches separately analyze the grouting parameters such as grouting,grouting pressure,grouting material and so on,which affect the deformation and stress of the strata.At the same time,due to the special engineering geological and hydrogeological conditions in Taiyuan,the influence of the post grouting on the deformation and the displacement of the soil should be paid more attention to in the construction of the subway tunnel.Based on the theoretical analysis and numerical simulation,this paper takes the west station of Taiyuan metro line two was taken as an example to analyze the soil stress and steady state in the process of shield tunnel construction.And the Results show that the stress concentration occurs in the face of tunnel excavation.And the tunnel excavation causes the shear failure of soil and surface soil in a certain range.Besides,with the advance of the shield,the range of the instability failure of the soil around the tunnel is small.And the plastic yieldrange of the surface is gradually extending to both sides.The stiffness transfer method was used to simulate the shield tunnel construction,and the transverse and axial surface settlement and the displacement of the segments are revealed.Lateral surface subsidence is symmetrical "groove" type.That is to say,the settlement of the upper part of the tunnel axis is the most significant,and the deformation of the formation decreases with the increase of the distance from the axis,which tends to be stable after a certain range.The main influence area is 20m(3D)from the tunnel axis.Besides,The axial surface settlement is relatively small along the direction of the tunnel,which is "S" curve in the process of shield propulsion.In addition,the deformation of the whole segment is the top segments sink,the bottom segments are floating,and the left and right side segments produce displacement away from the tunnel axis.There were significant differences between considering and not considering slurry solidification in Lateral and axial surface subsidence and segment displacement.Therefore,the stiffness transfer method is essential in the simulation of the whole process of shield construction;The effects of grouting amount,grouting pressure,grouting material elastic modulus,Poisson’s ratio on transverse,axial surface deformation and segment displacement were studied respectively.It shows that the increase of grouting parameters can effectively control the lateral and axial surface subsidence and the subsidence of the top segment.However,The displacement of the bottomsegment and the displacement of the right and the left segments increase with the increase of grouting parameters.The grouting parameters have the greatest influence on the floating of the bottom segment,and the displacement of the right segment is the least.Through the comprehensive analysis of the influence of the grouting parameters,the grouting amount should not exceed 150%.And the grouting pressure should be 0.35-0.45 MPa.Besides the elastic modulus of grouting material is 1.0-1.5MPa.In addition,the Poisson’s ratio should not exceed 0.3.Taking the maximum horizontal surface subsidence,the maximum axial surface subsidence and the ascent of the bottom segment as indexes,The influence of grouting parameters on the deformation of tunnel and ground surface was analyzed by orthogonal test,and the relationship between the deformation of tunnel and ground surface and the grouting parameters was obtained by multiple regression method.The results show that the influence of grouting parameters on the lateral,axial surface settlement and the floating of the bottom segment is as follows: the grouting quantity,the elastic modulus of the grouting material,Poisson ratio,grouting pressure.By dividing the grouting layer into two parts,The influence of uneven grouting was researched on the settlement of ground surface and segment displacement,which can provide references for the follow-up project construction.The results show that the uneven grouting does not affect the overall deformation of surface settlement.the surface subsidence can becontrolled by the uneven super grouting and uneven grouting pressure of which the upper half is smaller than the lower half.However,the uneven grouting of which the upper half is smaller than the lower half will aggravate the floating of the bottom segment.