Study On Mechanical Characteristics And Surface Settlement Law Of Super Small Radius Curve Shield Tunnel Segment In Water-rich Fine Sand Layer

This thesis takes the shield section of the connecting line of Taiyuan Metro Line2～1 as the engineering background.The radius of the tunnel curve is only 200 m,and the crossing stratum is mainly water-rich fine sand stratum.Compared with the straight shield tunnel,the ultra-small radius curve shield tunnel needs to be corrected in time for each excavation ring.The thrust of the outer jack of the curve is greater than that of the inner side,and the inner side of the curve has a large amount of over-excavation,high construction risk and difficulty.Therefore,the research on the ultra-small radius tunnel has important theoretical and engineering practical significance.According to the characteristics of ultra-small radius tunnel construction,the finite difference software FLC3 D is used to establish the numerical model.Combined with the field monitoring data,the single factor analysis method is used to study the influence of soil pressure,grouting pressure,jack thrust and inclination angle on the surface settlement law and segment stress characteristics during the construction process,and the corresponding construction technology control measures are put forward.The main research results are as follows:(1)During the forward excavation of the shield machine,the tunnel vault settlement and arch bottom uplift area gradually lose symmetry,and the peak position of the surface transverse settlement trough gradually shifts to the inside of the ultra-small radius tunnel curve.The unbalanced thrust of the jack is positively correlated with the offset distance of the peak position of the surface transverse settlement trough,while the grouting pressure,soil chamber pressure and jack thrust inclination angle have little effect on the offset distance of the peak position of the surface transverse settlement trough.(2)With the increase of the earth pressure,the surface settlement decreases first and then increases.When the earth pressure is 0.20 MPa,the surface settlement caused by construction is the smallest.With the increase of grouting pressure,the surface settlement gradually decreases,the segment dislocation gradually increases,and the principal stress of the segment is basically unchanged.The total thrust of the jack is positively correlated with surface subsidence,segment dislocation and principal stress,and has a significant impact on the three.When the total thrust of the jack exceeds a certain threshold,the rate of surface subsidence and segment dislocation change increases significantly.On the premise of meeting the specification standards,the reasonable configuration range of the jack thrust is determined to be 15 000 k N～21 000 k N.(3)Considering the influence of various factors on surface subsidence and segment faulting,the sensitivity is analyzed by orthogonal test method,and a set of tunneling parameter combinations with the least influence on surface subsidence and segment faulting are obtained.The fitting formulas between various factors and surface subsidence and the maximum value of segment faulting are proposed respectively.(4)By comparing the field monitoring results with the numerical simulation results,the applicability of the numerical simulation method and the reliability of the simulation results are verified.Combined with the engineering practice,the reasonable control range of construction parameters suitable for this project is determined,and the construction control measures are put forward from three aspects:stratum deformation,segment lateral deformation and segment floating,which provides reference for the construction of similar projects.