Study On The Deformation Behavior Of Shield Tunnel Structure During Construction Period In Soft Soil

With the continuous development of urban subway projects,the deformation of tunnel structure in soft soil is becoming more and more prominent.At present,most researches on tunnel deformation focus on surface subsidence.However,there are relatively few studies on longitudinal settlement and lateral convergence deformation of tunnel structures.Inhomogeneous deformation of the tunnel structure in a weak formation can lead to leakage of the segment.In severe cases,the segment can be damaged,resulting in loss of life or property.Therefore,it is an important research direction for the subway shield construction process to study the structural deformation law of the tunnel structure in the soft soil layer during construction and take measures to reduce the structural deformation in a timely manner.Based on the theoretical calculation model,this paper introduces the calculation model of longitudinal subsidence and transverse convergence of tunnel.On the basis of the longitudinal equivalent continuous beam model,the calculation theory of the sedimentation-strain model is given in detail,based on the monitoring wavelength of the optical fiber sensor in a certain tunnel,and the longitudinal matrix coefficient is proposed to simplify the calculation.At the same time,based on the constant stiffness continuous ring model,the conjugation-strain model is introduced in detail.Two radial displacement matrix coefficients are proposed to simplify the calculation process,and it is convenient to use computer to calculate.On the basis of theoretical analysis,a distributed optical fiber sensor is used as the monitoring element to monitor the deformation of the tunnel structure in Foshan.Through the analysis of the longitudinal/transverse strain,curvature,longitudinal/transverse joints,longitudinal settlement,lateral convergence and other monitoring results of the tunnel structure,the structural deformation law of the tunnel in different strata and different burial depths is studied.The comparison of optical fiber monitoring results,conventional instrument monitoring results,and numerical simulation results is performed to verify the accuracy of optical fiber sensor monitoring and the further study of tunnel structure deformation laws.By formulating the corresponding matrix coefficients,the calculation process of the longitudinal settlement calculation model and the lateral convergence calculation model are simplified,and it is convenient to use the computer to calculate.In the soft soil of the silt soil,the tunnel structure gradually rises in the week after the installation of the tunnel tube,and then gradually sinks under the effect of soil consolidation.At the same time,the better the soil quality,the smaller the uneven settlement.With the increase of burial depth of the tunnel structure,the longitudinal settlement gradually decreases,but the decreasing extent tends to slow down.The tunnel segment will be flattened into an ellipse.At the same time,in the condition of poor soil layer and shallow depth,the lateral convergence of the tunnel is mainly affected by the first tunnel excavation.Under the condition of good soil layer and deep burial depth,the lateral convergence of the tunnel is mainly affected by the second tunnel excavation.