| With the rapid development of society since modern times,the construction technology of subsea tunnels has made great progress.At present,the construction of subsea tunnels in my country mostly adopts the shield method.The shield tunnel structure is located in the underground environment,the geological conditions are complex,and earthquakes occur frequently in my country,and the structure is more significantly affected by earthquakes.Therefore,the analysis of the structural mechanical characteristics of the shield tunnel has become a key research topic.As a commonly used segment joint,bolts are easily damaged during use.As the force and bending moment on the segment joint increase,the bending stiffness of the bolt is also affected,which easily leads to the opening of the segment joint.and deformation,thus affecting the overall safety performance of the tunnel.Therefore,in-depth exploration of the mechanical properties of joints is an effective means to solve structural stability.In addition,tunnel earthquake damage is one of the most common important disasters in engineering.The earthquake action seriously affects the lining safety of the tunnel structure.Especially in the fault section,the phenomenon of tunnel earthquake damage is significantly aggravated.Response laws are less studied.In view of the above problems,this thesis relies on the national key research and development program "key technology for subsea tunnel construction and toughness enhancement",based on the ABAQUS software to establish a three-dimensional refined model of the segment joints,considering the influencing factors such as the joint longitudinal seam and bolt preload,etc.The mechanical characteristics of joints with two different types of bolts(slanted bolts and straight bolts)commonly used are analyzed.At the same time,the influence of the fault fracture zone on the safety of the tunnel structure was studied,focusing on the analysis of the internal force of the bolts in the fault section under the earthquake and the response law of the overall structure of the tunnel under different fault dip angles,and the following research conclusions were obtained:(1)Under the combination of loads,the stress of joint bolts increases with the increase of vertical load,and the change law of inclined bolts and straight bolts shows a consistent trend.Stress concentration occurs at the joints of the bolts.(2)At the initial stage of loading,the inner side of the segment is opened under the action of positive bending moment,and the outer side of the segment is opened under the action of negative bending moment.,the bending stiffness of the joint decreases gradually,and the vertical displacement of the overall structure increases suddenly.(3)Under earthquake action,the acceleration response of the tunnel in the fault section is larger than that in the normal surrounding rock area,the acceleration response peak value of the hanging wall surrounding rock tunnel is second,and the footwall is the smallest.The hanging wall tunnel is more prone to instability than the foot wall tunnel under earthquake action.Under different geological conditions,the maximum principal stress reaches its peak at the arch foot.The monitoring positions of the fault segment are 55%～72% larger than the hanging wall,and 50%～60% larger than the footwall.(4)In the seismic response,the axial force of the joint bolts at the vault is significantly greater than that at other positions,and the axial force of the bolts at the invert is the smallest.The bolt axial force in the fault section is greater than that in the ordinary surrounding rock section,and the bolts at the vault position in the fault section increase by 17.5% compared with the upper wall section,and increase by 28.5%compared with the lower wall section.(5)The structural stress of the segment lining is significantly affected by the fault dip angle.With the increase of the fault dip angle,the peak acceleration of the tunnel in the fault section decreases gradually.The peak accelerations of different fault dip angles are 45°,75°,and 90° from large to small.Under different fault dip angles,the variation trends of the lining principal stress along the tunnel axis are similar,and they all have obvious amplification effects at the fault fracture zone. |
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