Test And Numerical Simulation Of Mechanical Properties Of Shield Tunnel Segments Strengthened By Internally Bonded Steel Plates

With the increase in the population of large and medium-sized cities and the increase in urbanization,the contradiction between the rapid development of urbanization and the rapid growth of residents’ travel demand has become increasingly obvious.Rail transit lines have not only solved many problems such as traffic congestion,energy consumption and environmental pollution,but also contributed to guiding land development,optimizing urban structure,and conforming to the concept of urban sustainable development.Among them,the shield method has become the preferred method of subway construction in my country because of its high construction safety and less influence from the outside world.However,with the progress of track operation and structural service,many subway lines in the first-tier cities such as Beijing,Shanghai and Guangzhou have entered the "old age" period.In Nanjing,Suzhou and other cities,cracks,water leakage and radial deformation also appeared in subway tunnels due to uneven overloading and construction of adjacent rail lines.Since the structure is deeply buried in the ground and cannot affect the normal operation,it is not feasible to replace the damaged part,so the secondary lining reinforcement and maintenance have to be considered.Based on the structural safety protection research project of urban rail transit engineering in Xuzhou City,this paper took two types of full-scale standard block segments of intermediate and ultra-deep burying as the research object,and studied the reinforcement effect of internally bonded steel plate reinforcement on pipes with different buried depths and different damages.This research used a combination of experiment and ABAQUS numerical simulation to analyze and find the best steel plate reinforcement thickness and reinforcement time from the perspectives of tube displacement,steel bar stress and strain,and steel plate stress and strain,and explored the failure characteristics of steel plate reinforced arc tube structure.This paper also introduced digital image correlation technology(DIC)in the experiment to obtain the displacement field and strain field of the whole process of tube bending test,which overcomes the time and space limitations of the original strain gauge data collection.The main work was as follows:1.Bending mechanical test of unreinforced standard block segmentTwo-point flexural static test was performed on two segments with different buried depths,the failure characteristics of the segments and the development of cracks were observed during the test,and the concrete strain,the stress and strain of the internal steel bars and the displacement of the segments were measured.Preliminary research has been conducted on the failure rules of the buried B-type segment and the ultra-deepburied D-type segment.Provide experimental basis for the establishment and optimization of subsequent numerical simulation models.2.Bending mechanics test of standard block segment reinforced with steel plateLoad the segments in advance to make them have initial damage,and then reinforce them with steel plates.It was selected to carry out the two-point flexural test after reinforcement that the middle buried segment with initial damage degree of 78%and the ultra-deep buried segment with initial damage degree of 90%.The failure characteristics were observed,the width and development of cracks were recorded,and the strain of concrete,the stress and strain of the internal reinforcement,the vertical and horizontal displacements of segments,and the strain of the reinforced steel plate were also measured.Explore the impact of the degree of damage on the reinforcement effect when the steel plates and segments of the same specification are used for reinforcement.3.The bending test of reinforced segment is simulated numerically and the factors affecting the reinforcement effect are explored.The finite element software ABAQUS is used to simulate the bending test of the buried and ultra-deep buried segments before and after the reinforcement,and output the vertical displacement of the reference point of the tube segment,the stress of the steel bar and the stress and strain cloud diagram of the steel plate in the result Visualization.Compared with the data of the previous experiment,it is found that the data fits well,which proves the rationality of the model.On the basis of this model,the thickness of steel plate and reinforcement time(existing damage degree of segments during reinforcement)were changed.Seven segments with different thicknesses from0 mm to 50 mm were selected,and four segments with different existing damages from0% to 80% were analyzed to extract segment displacement and reinforcement stress in the process of bending moment changing from small to large.After comprehensively considering the height of the tunnel section,maintenance cost and construction difficulty,the steel plate specification and segment damage degree with the best reinforcement effect are selected to provide an important reference for engineering practice.This paper has 54 pictures,11 tables,and 86 references.