| With the development of urban rail transit and the utilization of underground space,the construction of foundation pits near shield tunnels is becoming more common.Excavation of foundation pits will cause longitudinal deformation and lateral convergence of adjacent existing shield tunnels.In severe cases,it may even cause damage to the tunnel structure,which will cause safety hazards to the operation of the tunnel.In this paper,the deformation control parameters of the foundation pit enclosure structures are selected to establish a sidewall unloading model that can consider the deformation of the supporting structures and the spatial effect of the foundation pit,and divide the influence area of the sidewalls.A cooperative deformation model that can comprehensively consider the two deformation effects of shield tunnel segment ring rotation and dislocation is introduced,and the longitudinal force and deformation of side and lower shield tunnel caused by excavation of foundation pit are studied.Aiming at the variations mechanism of confining pressure of the side and lower shield tunnels caused by excavation of foundation pits,a calculation method of additional confining pressure variations of shield tunnels that can consider the forces between segment rings in longitudinal deformation is proposed to study the transverse force and deformation of the side and lower shield tunnels.Select corresponding engineering examples to verify the reliability of the calculation method in this paper,and analyze the influencing factors.The main research results and innovations of this article are as follows:(1)The longitudinal deformation of the shield tunnel beside and below the foundation pit is calculated by comprehensively considering the two deformation effects of segment ring rotation and dislocation.The calculation results are in good agreement with the measured values,which can reflect the actual deformation mode and law of the shield tunnel in such projects.At the same time,the rotation angle,dislocation and the shear force between segments can be obtained.(2)In the process of studying the transverse force of the shield tunnel beside and below the foundation pit,the calculation method of the transverse additional confining pressure variations of the shield tunnel is proposed respectively.This method considers the force between segment rings in longitudinal deformation and can describe the additional confining pressure redistribution process of force-displacement-rebalance of the shield tunnel beside and below the foundation pit.At the same time,the transverse force and deformation of the shield tunnel is analyzed,and the method is verified by engineering example analysis.(3)Through the research on the influencing factors of the shield tunnel beside the foundation pit,it is found that the longitudinal deformation of the tunnel is mainly caused by the unloading effect of the side wall of the foundation pit parallel to the tunnel;the excavation of the deep soil layer has a greater impact on the side shield tunnel;As the deformation of the foundation pit enclosure structure increases within a certain range,the longitudinal deformation and influence range of the tunnel also increase,and the absolute values of the additional confining pressure and additional bending moment of the segment rings increase significantly;The tunnel with the burial depth greater than the foundation pit excavation depth will significantly reduce the sensitivity to the impact of the side excavation.(4)Through the research on the influencing factors of the shield tunnel below the foundation pit,it is found that the increase in the excavation size of the foundation pit in all directions within a certain range will increase the uplift value and uplift range of the shield tunnel below the foundation pit,and also increase the absolute value of the additional confining pressure,the additional bending moment and the additional convergence value of the shield tunnel below the foundation pit.Three-dimensional unloading ratio V3D is more suitable to the evaluate the influence of the longitudinal deformation for the shield tunnel;The spatial dimension coefficient Vc of the foundation pit can be used to evaluate the transverse force and deformation of the shield tunnel below the foundation pit. |
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