Seismic Response Analysis Of Shield Tunnel In Underwater Saturated Ground Site

The seismic response of shield tunnels in a saturated underwater site is a crucial problem to be solved in constructing large-scale cross-river and cross-sea projects in China.However,due to the wide range and difficulty of the research problems,the research results are relatively few.Therefore,it is significant and urgent to study the seismic response of underwater shield tunnels.This paper studies the seismic response of shield tunnels in saturated underwater sites by combining theoretical analysis and numerical simulation.The main research work and achievements of this paper are as follows:(1)According to the law of traveling wave propagation,the existing 1D time-domain method for calculating underwater free site response is extended to two and three-dimensional space.With the support of a viscous-spring dynamic artificial boundary,the accurate input of wave is realized by combining the artificial boundary substructure model.A seismic wave input method is established for solving the underwater dynamic interaction of saturated soil and structure.The reasonability and accuracy of the site expansion process,application of viscous-spring artificial boundary,and seismic wave input are verified by numerical examples,which lays a foundation for subsequent research.(2)In the aspect of transverse seismic of shield tunnel,a dynamic interaction model of the underwater saturated soil-tunnel structure is established.The effects of plane wave incidence in different water depths on structural displacement,Mi Ses stress,and bending moment are analyzed by considering site conditions,incident wave characteristics,and structural characteristics.The results show that the stress concentration at the structure’s arch shoulder and arch foot is evident,which are more prone to damage under earthquake waves.The seismic dynamic response of the structure is significantly affected by water depth,seismic wave type,incident Angle,buried depth of the structure,lining stiffness,and the location of monitoring points.Among them,seismic wave type,incident Angle,and buried depth greatly influence internal force and displacement of the structure.Lining stiffness and water depth have little influence on structural displacement but a significant influence on the internal structural force,and it is necessary to consider the oblique incidence of seismic waves and the variation of water depth.(3)In the aspect of longitudinal seismic of shield tunnel,a three-dimensional refined finite element model containing soil,segment,and longitudinal joint bolts is established.The influences of different incident Angle,directions,and overlying water depth on the internal force and deformation of longitudinal joint bolts were analyzed.At the same time,the segment opening amount and stagger amount,which are concerned in engineering,are discussed.The results show that under the action of the P wave,the internal force of bolts at the shoulder and foot is large,and the opening amount and stagger amount at the waist is large.Under the action of SV wave,the internal force of bolts at the waist of the arch and the segment opening amount is large,and the shoulder and foot of the arch are large.The internal force and deformation of the longitudinal bolt,the opening of the segment,and the amount of misalignment are related to the incident Angle,incident direction,and the position of the monitoring point,and the water depth is relatively less affected.The relatively flexible tunnel should be used in the design,and the flexible joint should be set appropriately so that the structure can better adapt to the stratum deformation.