| At present,the subway construction is developing rapidly,and the shield tunnel construction is developing towards the trend of "more and more buried depth,longer and longer lines and more and more complex lines".Especially when the shield passes through the soft stratum of saturated soil with high moisture content such as silt clay and soft soil,the attitude of the shield will inevitably change,and the disturbance to the surrounding soil will further increase.In addition,the new shield tunnel line will pass through complex geological conditions and avoid the existing underground structures,and the tunnel shield construction with small curvature radius curve and construction along a certain slope will be more and more,thus the influence on the surrounding environment will become more prominent.Therefore,it is of great engineering significance to study the soil deformation caused by the attitude change of shield.This paper focuses on the influence of shield attitude on surface deformation in saturated soil,fully considers the mechanical characteristics of non horizontal and non-linear shield driving conditions,corrects the main construction influencing factors,and obtains the theoretical calculation formula of shield upward tunneling and small curvature radius curve shield tunneling.Combined with the measured data and numerical simulation results,the accuracy of the prediction formula is verified The main research contents and conclusions are as follows:(1)The deformation law of soil caused by shield construction in different stages is analyzed by selecting the interval with large shield attitude change.Due to the change of shield attitude,the lateral settlement trough will also shift to one side of the tunnel.By comparing the measured results with the prediction results of double track peck formula,the applicability of double track peck formula to the prediction of cross line surface deformation of double track shield construction is verified.(2)Taking full account of the construction characteristics of non horizontal shield tunneling,a mechanical model of upward shield tunneling with a certain slope is established.Considering the influence of various construction factors on the surface deformation,the values of main construction parameters are modified.Based on the initial solution of saturated soil in semi infinite space,the theoretical prediction formula of surface deformation caused by upward shield tunneling is obtained,which is compared with the classical min With the increase of shield elevation angle,the curve of surface heave and settlement caused by additional thrust of the incision tends to move up to the right,and the curve of longitudinal surface deformation tends to move up as a whole.(3)The theoretical prediction formula of surface deformation caused by shield tunneling in curved tunnel is obtained by fully considering the factors such as uneven thrust of excavation face,uneven friction of shield shell and over-excavation inside the line.Overexcavation of the inner soil in curved tunnel shield tunneling will cause the surface deformation settlement trough to shift to the inner side of the line.The settlement trough offset is affected by the thrust difference between the left and right cutterheads and the total thrust of the cutterhead,and the change of turning radius will not affect the degree of surface transverse settlement trough offset.Cutter head diameter has a great influence on the offset degree of surface transverse settlement trough,and the surface settlement deformation is greatly influenced by the change of shield shell length.The shorter the shield shell length,the smaller the surface settlement deformation.(4)A refined numerical model of shield tunneling with small curvature radius curve is established by coupling shield machine,segment,segment connecting bolt,internal stress reinforcement,slurry and water and soil pressure.The ground deformation,shield tail segment displacement,tunnel section convergence,deformation and stress changes of connecting bolt and reinforcement in segment during shield tunneling with small curvature radius are analyzed.Further explore the shield tail segment floating law and the internal force variation characteristics and laws of segment,reinforcement and bolt,and optimize the segment structure. |
