Analysis Of The Influence Of Construction Load On The Longitudinal Internal Force Of Shield Tunnel

Although a large number of shield tunnels have been constructed,the theoretical understanding of segment lining structure of shield tunnels is not deep enough.There are many joints in the segmental lining of shield tunnels,which have a direct impact on the mechanical properties of the tunnel structure,especially the influence of load on the structure during the construction period has not been fully understood.This paper focus on the longitudinal internal force of shield tunnel under construction load.Firstly,the load characteristics during construction period are analyzed,and the influence of the jacks and simultaneous backfill grouting is the main factors.Secondly,the commonly used models are analyzed from several aspects,and the shortcoming of these models is stated.And then,improvement is introduced to the commonly used equivalent beam model from three aspects,including the consideration of ring joint,the action of jacks,and the influence of simultaneous backfill grouting.After the including joint spring,the nonlinear behavior of ring joint can be simulated through the iteration process,so this model can show whether the ring joint is at close state or open state and obtain the open value.Based on the Yangtze River Tunnel Project,the influence of the non-linear characteristics of circumferential joints on the longitudinal internal forces of shield tunnels is analyzed.The results show that under the influence of non-linear stiffness of joints,the value of internal force and influence range are smaller than those of the traditional equivalent homogeneous beam model,but the deformation of the structure increases.Compared with the equivalent beam model,the improved longitudinal beam spring analysis model of shield tunnel has smaller longitudinal bending stiffness.In addition,aiming at the influence of Jack action and synchronous grouting,the load during construction period is further studied by parameter analysis.It shows that the internal force and deformation of shield tunnels will occur in a certain range under the additional action of grouting load and jack load.Compared with the grouting effect,the additional bending moment and shear force exerted by jack have a more significant influence on the internal force of segment,and have a certain influence on its distribution range,but the influence is limited.Under the influence of the change of the length of the area affected by synchronous grouting,the structural displacement changes significantly,the bending moment is affected to a certain extent,and the shear force changes insignificantly.Under the restriction of the force of jack,the annular slit of segment is possible to open,and the controlling factor is the shift of the longitudinal jack force,that is,the additional bending moment imposed by jackers on segment structure,the opening of annular slit mainly occurs near the tail of shield.In addition,based on the analysis of the mechanical behavior of the segment lining structure near the shield tail during the construction period,the shell spring model of the structural analysis during the shield construction period is established to realize the fine simulation of the interaction between segmental rings.Based on Shanghai Yangtze River tunnel project,the deformation characteristics and internal force of shield tunnel segment lining structure are studied from two aspects,that are the effect of synchronous grouting and interaction between rings.The results show that the area of synchronous grouting will lead to the staggered movement of segment lining structure.In addition,the bending moment and axial force of segment structure in the influence area of synchronous grouting are greater than the bending moment and axial force under design load.With the increase of the length of the non setting area of synchronous grouting,the number and momentum of the staggered circular joints increase.However,if measures are taken to reduce the length of the non setting synchronous grouting area,increasing the interaction between the circular joints(increasing the friction coefficient of the circular joints or increasing the longitudinal force)can reduce the number of circular joints and the staggered area.