Research On Optimization Design Of Geometric Progression Layout Of Shield Thrust System Under Mixed Ground

When shield tunneling is carried out under the condition of composite stratum,the traditional uniform thrust system and the zonal thrust system are easy to generate biased load under the coupling action of external loads due to the uneven stratum and the great difference in rock-soil strength.However,too much biased load will easily cause uneven stress on the rear segment,resulting in displacement or collapse of the segment and ultimately affecting the construction quality of the tunnel.Therefore,it is more and more important to optimize the layout of the thrust system.This paper focuses on the in-depth study for the construction of the mechanical model of thrust system in shield machine and the analysis of force transfer performance.Based on these theoretical foundations,the geometric progression non-uniform optimal layout model is proposed,and the anti-biased load performance of the geometric progression layout model is finally verified through comparative analysis from the finite element.The mechanical model of shield thrust system is constructed.The external loads of shield tunneling in composite formation are analyzed in detail,and the formation mechanism and influencing factors of the biased load of the thrust system are expounded.Based on the above research,the dynamic equilibrium equation of the shield thrust system is established.The force transfer performance of different thrust systems in shield machine is studied.Based on the established mechanical model,the thrust optimization function is constructed based on the uniformity principle of jacking force provided by the segment,and then the Lagrangian function is further obtained.By solving the partial derivatives of the established Lagrangian function,the thrust spacial ellipse models of uniform thrust system,six-zone thrust system and non-uniform thrust system are constructed.Taking the constructed elliptic eccentricity as the evaluation index of the force transfer performance of the thrust system,the force transfer characteristics of the shield thrust system under above three layouts are analyzed in detail.Based on the analysis of the force transfer characteristics of the shield thrust system,a non-uniform layout optimization design method is proposed.According to the thrust spacial elliptic model established in chapter 3,and based on the principle of elliptic eccentricity equal to zero,the geometric progression layout model of the phase angle difference of two adjacent hydraulic cylinders is established.The geometric progression layout optimization design method is applied to the construction case of tunnel in Dusseldorf,Germany,and the force transfer performance of optimized thrust system is compared with that of the six-zone thrust system to obtain the stratum adaptability of these two kinds of layouts under composite stratum.Finally by the ABAQUS finite element software,the comparative simulation analysis about the stress of the segment is carried out to verify the ant-biased load characteristic of the geometric progression non-uniform layout design method.Based on the measured thrust data,through finite element analyzing for rear segments from the uniform thrust system,the six-zone thrust system,and the thrust system optimized by geometric progression layout methods,the deformation and the stress of segment under the three layout systems is given to verify the effectiveness of anti-biased load performance of the non-uniform layout design method.