Analysis On Mechanical Properties Of The Segment Structure In Shield Tunnel When The Joint Bolt Was Damaged

Since the 21st century,China has accelerated its urbanization process,in order to alleviate the traffic congestion caused by the rapid development of urbanization,Metro projects have been extensively constructed.At present,the main construction methods of subway include open-cut method,top-down method and subsurface excavation method,shield tunneling is the main construction method of subway in China.The lining structure of the shield tunnel is formed by many segments connected through the joints,therefore,joints play an important role in the segment structure,once the joint is damaged,the safety and stability of the segment structure will be seriously affected.Nowadays,there are few researches on the causes and treatment measures of the joint bolts' s damage in the shield tunnels both at home and abroad.The effect of bolt breaking on mechanical behavior of the linging structure is not clear.So,based on the engineering practice,this paper has carried out the research on the causes and treatment measures of the bolt damage in the shield tunnel,and the effect of bolt breaking on mechanical behavior of the linging structure is analyzed by numerical calculation.The main research work and related achievements of the paper are as follows:(1)Through literature research and combined with practical engineering,the causes and treatment measures of the bolt damage is summed up.The factors affecting the safety and durability of joint bolts include material factors,environmental factors and construction factors,etc.When the bolt is broken,the usual treatment measures include steel plate reinforcement,carbon fiber reinforcement and so on.(2)Through the numerical calculation,the difference of mechanical behavior of segment structure is analyzed before and after the joint bolts is broken.It is concluded that when the bolt is broken,the tensile stress and compressive stress of the segment change little.And it can be seen that after the completion of the construction,when the grouting is full behind the segment and the quality of the segment meets the requirements,the bolt has little influence on the the segment.After the bolt is broken,the shear and deformation of the lining are increased to a certain degree,part of the shear force originally assumed by the bolt is now carried by the segment.If the quality of the tube or the quality of the construction is not up to the standard,the phenomenon of torsion and misalignment can easily occur in segment structures,resulting in instability and failure of lining structures,which should be eliminated in Engineering.(3)Taking into account that the broken joint bolst are located in the alternation of Grade IV and Grade V surrounding rocks,the grade of surrounding rock on both sides of the joint bolt may be different.It is calculated that both the stress and deformation of the segment structure in the heterogeneous stratum are greater than that in the homogeneous stratum no matter before or after the bolt is broken.This is because in the hard and soft alternating strata,the uneven stress of the segment structure causes the segments and joint bolts to bear more shearing force.Thus,the torsion of the structure is increased,and the internal force and deformation of the segment structure increase correspondingly.