| Shield tunnels have been increasingly used in urban rail transit.After completion of construction,shield tunnels will deform under different loads such as assemblycaused axial force,ground surcharge,uneven settlement of underlying soil layers,adjacent constructions and so on.Large deformation may cause damage to buried pipelines,affect normal production and life,and even bring about loss of life and properties.Therefore,it is significant to find a way to determine the settlement of shield tunnels.In this paper,the settlement of shield tunnels was studied by combining theoretical analysis,numerical simulation and field measurement.A mathematical model to the settlement of shield tunnels,considering bending-deformation-caused axial force and shear effect,was established.A Fourier series solution for the mathematical model was given.The law of settlement of shield tunnels under different influencing factors was discussed,and the calculation results by the series solution were compared with that by field monitoring.The main results are as follows:(1)The results by the Fourier series solution of this paper are well consistent with that by existing analytical solutions and finite element numerical simulations.(2)The influences of end bearing conditions,types of the load,length-to-height ratio and shear stiffness of the tunnel,the width of settlement trough,the settlement and subgrade coefficient of the soil layers on the settlement of the tunnel are as follows:1)Under the condition of fixed support at both ends,the shear deformation accounts for the largest proportion to the total deformation;2)The greater the load is applied in the middle of the span,the greater the proportion of shear deformation;3)The smaller the length-to-height ratio of the tunnel,the larger the proportion of shear deformation;4)Shear effect makes the total deflection to increase and,at the same time,the bending deflection and bending moment to decrease;5)The smaller the shear stiffness is,the larger the shear deformation gets,and the larger the proportion of the shear deformation becomes as well.The proportion of the shear deformation can reach more than 25%;6)The larger the assembly-caused axial force is,the greater the total deformation gets.However,the assembly-caused axial force doesn’t have significant influence on the deflection and bending moment,which account for no more than 2% and no more than 3%,respectively;7)The settlement of soil layer at the midpoint of the trough has no obvious effect on the proportion of shear deformation;8)The wider the settlement trough,the smaller the proportion of shear deformation;9)The larger the subgrade coefficient,the larger the proportion of shear deformation.(3)In case studies,the results by series solution were compared with that by field monitoring and that by finite element numerical simulation,which gives a good agreement with each other.It shows that the proposed method can be used to calculate the settlement of shield tunnels in practice. |
