Research On Influence Of Surface Surcharge On Existing Shield Tunnel

With the continuous improvement of the urban underground transportation network,more and more construction works are carried out next to existing subway lines,and the problem of sudden surface surcharge is becoming more and more serious.On the one hand,surface surcharge will cause uneven longitudinal settlement of the existing shield tunnel below;on the other hand,the lateral force and deformation of the shield tunnel will change significantly under the surcharge.Therefore,it is necessary to carry out a comprehensive study on the influence of surface surcharge on existing shield tunnels from both vertical and horizontal directions.At present,most researches on the influence of surface surcharge on existing shield tunnels focus on the longitudinal direction of the tunnel.The shear effect of the shield tunnel and the continuity of foundation deformation are often ignored in the theoretical derivation.In addition,the research on the lateral force and deformation of the tunnel under the ground surcharge is less than that on the longitudinal direction of the tunnel,and the traditional modified idioms are mostly used in the theoretical calculation process,which can not reflect the influence of segment joints on the bearing capacity of the segment lining ring.Based on the existing theoretical research results and the deficiencies of the existing research,this paper proposes related calculation models to comprehensively study the influence of surface surcharge on existing shield tunnels from two perspectives: vertical and horizontal.The reliability of the theoretical calculation model is verified based on the publicly reported and published engineering cases.The main work and research results of this paper are summarized as follows:(1)Based on the existing calculation theory of longitudinal deformation of shield tunnels under surface surcharge,considering the weakening of shear stiffness of the whole shield tunnel due to the existence of connecting bolts and the continuity of foundation deformation,the shield tunnel is simplified as Timoshenko beam on the Pasternak foundation model(defined as T-P model in this paper).Based on the T-P model,the differential control equation for the longitudinal deformation of the existing shield tunnel under the surface surcharge is derived,and the numerical solution is obtained using the finite difference principle.Then,the applicability of the model is verified by comparing the theoretical calculation results with the actual monitoring data.(2)Based on the full-scale test of segment joint of Shanghai Metro through joint assembly shield tunnel,the nonlinear bending stiffness model of segment joint is analyzed and extracted,and the beam-nonlinear spring model which can accurately describe the bearing mechanism and deformation mode of segment lining ring of shield tunnel is established.Based on the actual case of ground surcharge,the reliability of the beam-nonlinear spring model is verified,and the characteristics of transverse force and deformation of shield tunnel before and after surcharge are compared and analyzed according to the calculation results of the model.(3)A calculation example of the ground surcharge is established.The above theoretical calculation models are adopted to discuss the influence of the ground surcharge on the longitudinal and transverse deformation and stress of the existing shield tunnel when the key factors such as the location and size of the surcharge,the nature of the stratum where the shield tunnel is located,and the structural parameters of the tunnel change.The relevant results can provide some reference for the engineering construction.(4)The common diseases of shield tunnel under the surface surcharge are summarized.This paper analyzes the reinforcement mechanism of shield tunnel and the advantages and disadvantages of various reinforcement measures.In view of the commonly used steel plate reinforcement method in the actual project,a reinforcement structure analysis model is established which can consider the bond performance between the reinforcement steel plate and the tunnel segment,and the reinforcement effect of the steel plate reinforcement method is evaluated using the proposed structure model,which proves the effectiveness of the method.The paper has 72 figures,7 tables,and 90 references.