A Study On The Influence Of Tunnel Cavity Defect On Lining Structure And Its Crack

In recent years,Tunnel and underground engineering construction is booming in our country.Subjected to a number of adverse factors,a substantial proportion of built tunnels or operating tunnels have cavity quality defects.The tunnel cavity defect has the characteristic of covertness.It does not directly constitute the lining structure disease entity,but it causes the lining structure suffering damage indirectly.The potential damage is enormous.Therefore,it is of great significance to study the damage of tunnel lining structure under the condition of tunnel cavity defect,which is helpful to clarify the mechanism of tunnel cavity damage.Considering this,this paper,on the basis of previous studies,using the research methods such as investigation,theoretical analysis and numerical simulation does following works:(1)The cause and damage of tunnel cavity are systematically studied and analyzed,and the mechanism of structure collapse induced by tunnel cavity is revealed from the angle of the mechanism between surrounding rock and support interaction.(2)Studies are made on the impact of lateral and vertical dimension parameters of tunnel cavity on internal force of lining structure in the horizontal stress field and self-weight stress field.In addition,influence of relative strengths of lateral and vertical dimension parameters on the internal force of lining structure is analyzed.The results show that:1)in the two sorts of in-situ stress field,the bending moment of the lining structure within the range of cavity and its adjacent area increases linearly with the increase of the lateral or vertical dimension of cavity;2)the influence of the transverse diameter of vault cavity on the internal force of the lining structure is stronger than the influence of the vertical size of vault cavity on the internal force of the lining structure in the two sorts of stress fields.(3)Based on the ground-structure model,use a new theory for simulating material fracture—extended finite element method(XFEM)to study the distribution of cracks in lining structure and the damage of tunnel structure in the horizontal stress field and self-weight stress field when there is a single cavity or combined cavities behind the lining.The results show that:1)under the self-weight stress field,the lining structure is more likely to be cracked but less likely to be crushed under the influence of tunnel cavity;2)under the horizontal stress field,cracking breakage of the lining structure is accompanied with crushing failure of the tunnel;3)tunnel lining is much different under the influence of tunnel cavity,and the tunnel cavity is more destructive to the lining structure under the horizontal stress field.(4)Through the analysis and study,the mechanism of tunnel cavity damage undergoes the following three stages:1)Early stage—the germination of the void and the extrusion deformation of the structure;2)Medium stage—tunnel structure deformation and fracture;3)Later stage—structural cracks extension.