Concrete Shrinkage Test And Crack Resistance Analysis Of Segment In Shield Tunnel

Based on a Yangtze River Tunnel Project in Nanjing,Jiangsu Province,through the concrete shrinkage test,the paper studies the influence of SRA on the shrinkage of concrete,and obtains the shrinkage prediction model by nonlinear regression analysis.The soft modulus method model,3D shield tunneling process model and shield tunnel segment local model are established by using ABAQUS large-scale general finite element software.The deformation,internal force of the lining ring in the maximum depth of the Yangtze River Tunnel under the coupling effects of self weight,surrounding rock action,water pressure and concrete shrinkage are established.The stress field and the distribution of cracks are simulated and analyzed.The main work and achievements are as follows:(1)The shrinkage test of concrete prism is carried out.The influence of the amount of reducing agent on the shrinkage rate of concrete is studied.The regression fitting is carried out by the exponential shrinkage prediction model,and the law of shrinkage age of concrete of each mix ratio is obtained.The conclusion is that with the increase of the amount of reducing agent,the shrinkage rate of concrete decreases and the ultimate shrinkage strain decreases with the increase of the amount of reducing agent.(2)The soft modulus method is used to analyze the excavation and lining support of shield tunnel.The stress release and displacement of surrounding rock caused by excavation,as well as the internal force and deformation of lining structure under the action of self weight,surrounding rock pressure and water pressure are simulated by FEM.The results show that the tunnel lining is a partial compression member,and the positive bending moment is applied at the arch top and the bottom of the arch,and the tension trend is found in the inner side of the segment;The bending moment of the arch waist on both sides is negative,and the outer side of the segment has the tendency of tension.(3)The 3D finite element model is established for the construction process of shield tunnel,and the load transfer of shield tunneling is simulated by using the life and death element.The stress and deformation of shield tunnel lining under the coupling of the construction and support process and concrete shrinkage effect are simulated and analyzed.The results show that tensile stress will appear in the lining arch top,the inside of the arch bottom and the outside of the arch waist.The shrinkage effect of concrete after the segment assembly can be effectively reduced by reducing the shrinkage agent and prolonging the curing time,thus reducing the additional axial force and bending moment of the lining segments.(4)Through the establishment of partial model of reinforced concrete in shield tunnel segment,the Extended Finite Element Method is used to analyze the concrete cracking of lining segments under the coupling of surrounding rock action,water pressure and self weight and concrete shrinkage effect.The results show that the quantity and development of cracks in shield tunnel segments can be reduced by reducing shrinkage agent and prolonging the maintenance time.The different rotating positions of the staggered joint assembly lining will change the distribution position of concrete cracks.