Research On The Mechanism Properties Of The Double-layer Lining Structure For Shield Tunnel

In recent years,China's shield tunnels is gradually developing towards deep burial,large section and ultra-long growth.The geological conditions and surrounding environment of tunnels have become increasingly complex.The single-layer lining structure has been difficult to meet the operational safety and structural durability of shield tunnels,the demand for double-lining structures is increasing.However,there are relatively few studies on the double-layer lining structure of shield tunnels,causing it difficult to provide a powerful guidance for the design and construction of the double-layer lining structure of shield tunnels.In view of this,this paper systematically studies the mechanical properties of the two-story lining structure of a shield tunnel,in terms of different types of double-layer lining,different scales of shield tunnels and the conditions of soft and hard composite ground conditions,relying on subway shield tunnels and high-speed railway shield tunnel projects,using theoretical analysis and model test methodology.The following main research results were obtained:(1)Considering the influence of segment joints of shield tunnels on the mechanical properties of segmental lining structures,a three-dimensional similarity test model is proposed to simulate the mechanical properties of double-layer lining structures of shield tunnels.According to the equivalent principle of flexural rigidity,using the inner and outer partition grooving method to simulate the segment joints in the equivalent way,using the joint piece to simulate the longitudinal joint of the segment lining,solves the simulation problem of the longitudinal joint of the lining segment of the shield tunnel,and perfectly reflects the segment joint local effect.(2)For two types of shield tunnel lining structures,superimposed and compounded clarifies the contact relationship between the layers,mechanical transfer mechanism and mechanical properties of the contact surface.The physical similarity simulation method of the two interlayer contact modes are respectively proposed.Also the double-layer lining structure of shield tunnel and double-layer lining structure of composite shield tunnel are constructed.(3)For the double-layer lining structure of shield tunnel,the segment lining is the main body of the load-bearing structure,the secondary lining being the auxiliary load-bearing structure,and the largest proportion of the external load of the secondary lining in the overlapped and composite lining structure respectively achieved 41.59% and 38.13%.The integrated lining structure has higher overall bearing performance,and the structural stress state is more favorable.The process from the local macroscopic crack to the overall instability is long.The longitudinal stiffness of the composite lining is small.Under the same load conditions,the tunnel clearance of the structure has a large convergence value and deflection,and its instability has an unexpected characteristic.(4)When the outer diameter of the shield lining double-lining structure increases from 6.8m to 10.8m,the average load of the secondary lining is increased from 30.59% to 33.15%,and the ultimate load-carrying capacity of the overall double-lining structure is increased.The structural ellipticity is respectively 44.8‰ and 79.12‰ when reached the critical instability state.With the increase of the outer diameter of the double-lining structure,the peak acoustic emission energy increases from 155 V·?s to 233 V·?s,which aggravates the damage degree of the lining structure.(5)When the shield tunnel is in an inhomogeneous of soft and hard stratum,the stress state of the double-layer lining structure located in the soft soil layer is more unfavorable.Under the same loading condition,the ellipsoidal change of the lining structure in the soft soil layer is more serious than in the hard soil layer,which results in the lining structure more easily reaching the destabilization and failure state in the soft soil layer.When the double lining structure is located in the soft soil and the hard soil layer,the peak acoustic emission energy is 274V·?s and 178V·?s,the damage degree of double lining structure is more serious when it is located in the soft soil layer.