Study On Mechanical Performance Of Linings Of Curved Middle Wall Multi Arch Tunnel With Voids Behind Lining

This paper uses literature review,mathematical statistics,inductive summary,numerical analysis and other methods are used to systematically study the mechanical characteristics of lining structure under the condition of voids behind the lining of double arch tunnel with curved middle wall.First,the distribution characteristics of lining damages of curved middle wall multi arch tunnel are statistically analyzed.On this basis,a three-dimensional finite element model is established to analyze the mechanical characteristics of tunnel structure under the condition of voids behind the lining.The extended finite element method is used to study the crack law of lining structure of multi arch tunnel under the influence of voids.The main conclusions are as follows:(1)Based on the statistical analysis of the distribution characteristics of lining cracks,water leakage,and voids behind the lining,the general laws of lining damages are obtained: the cracks are mainly distributed in the arch,the crack forms are mainly circumferential and longitudinal cracks,and the crack width is mainly distributed in 0 ～0.2mm.And the leakage water in the curved middle wall multi arch tunnel is mainly local wet immersion.The average longitudinal length of the void is 7.6m and the average vertical height of the void is 37.8cm.(2)On the basis of a curved middle wall multi arch tunnel project,a three-dimensional finite element model was established to analyze the mechanical characteristics of lining structure under the condition of voids behind the lining of curved middle wall multi arch tunnel.Research has shown that the existence of voids behind the arch lining causes the vault lining to appear "convex" phenomenon,and the local area on both sides of the void appears "concave" phenomenon,which changes the internal force distribution characteristics of the structure.The results showed that the stress performance of the lining is deteriorated and the overall bearing capacity of the tunnel structure is reduced.When the annular range of the void is increased,the eccentricity of the lining structure increases,and the mechanical performance of the structure deteriorates.Under the action of tensile stress,the lining structure is easy to crack.The increase of the longitudinal length of the void has a great impact on the distribution of axial force and bending moment on the same side of the lining structure.But when the length of the void is greater than 12 m,the lining structure will have a greater impact on the lining safety.The void at the arch of multi arch tunnel only has a great affects the deformation law and internal force distribution characteristics of the tunnel lining on the same side,and basically does not affect the safety of the tunnel lining on the other side.(3)The extended finite element method is used to analyze the cracking law of the structure of the curved middle wall double-arch tunnel under the condition of the cavity behind the lining.Mainly as follows: The size and distribution of the void will affect the cracking law of the lining of the curved double-arch tunnel.When there is a void in the single-sided tunnel vault of a curved middle wall double-arch tunnel,with the increase of the circumferential range of the void,the lining structure on the side away from the middle partition wall cracks first.And the crack initiation load and expansion depth of the arch lining structure decrease and increase respectively with the increase of the annular range of the void.When there are voids on the left and right sides of the tunnel,the deformation rules of the cracks on the outside of the vault is more complex than that of the single void.When the circumferential range of the two sides of the voids is different,the crack load of the arch lining on the larger side of the void is less than that of the smaller side,and the crack expansion depth is larger than the smaller side.With the increase of the load,the crack expansion rate of the lining inside the lining near the middle partition wall increases sharply,and the structural bearing capacity decreases sharply.