Study On Affecting Mechanism Of Tunnel Structure-System Safety With Voids Behind Lining

Voids behind lining are universal during the construction of tunnel. The mechanical performance of rock and lining is perfect while there is no void between them. But it is not the case when void exists. The voids behind lining will degenerate the mechanical properties both of rock and lining. The paper systematically studied the affecting mechanism of voids behind lining, by means of review of literatures, in-situ inspection and monitoring, theoretical deduction, numerical analysis and model test. The main research contents and conclusions are listed below.(1)The distribution character and law of common quality defect are similar between highway tunnels and railway tunnels.The paper analyzed the inspection data collected from 21 highway tunnels and more than 100 railway tunnels. Then the paper classified the common quality defects (the insufficient thickness of lining, cavities behind lining, etc.) and structural disorders (concrete carbonization, cracks in lining, etc.). Especially the voids and cracks, the paper described the distribution character of them in detail, and pointed out the interior relationship between voids and structural disorders.(2)Voids behind lining affect the interactive role between rock and lining, stress redistribution revealed the mechanical mechanism of voids behind lining. Using the model test and numerical calculation redistribution and law are obtained: ①Stess concentration appears near the voids for the redistribution of rock stress. ②The character of rock stress redistribution is the shape of single summit when there is only one voids; The character of rock stress redistribution is the shape of camel summit when there are two voids commonly, and the shape of single summit when two voids are very closely; Therefore, by the research of the changed load between rock and lining, the paper obtained the law that stress redistribution obeys and revealed the mechanical mechanism of voids behind lining.(3) There is an internal relationship between the properties of void and cracks of lining structure.The properties of void (size, position and spatial organization. etc.) dictate the influence effect of void. Hence, by means of 2D model, the paper conducted numerical simulation to explore the general law. Further, the paper utilized the extended finite element method (XFEM) to study cracks behind lining and obtained a general rule of crack position and its evolutionary process.(4)Rock stress redistribution should be considered when tunnel safty is calculated, load model should be modified when load-structure model is used. When load-structure method is adopted to evaluate the safety of lining, the value of load is the key. The load pattern was refined by means of model test and theoretical analysis, and based on which the load-structure method is corrected when voids behind lining exist. Finally, an example is presented to verify the practically utility and effectiveness of the pattern.(5)Engineering application.Supported by the renovation project of SangZhouling tunnel, the paper analyzed the stress state of lining before and behind reparation by numerical simulation and in-situ monitoring. The relationship between cracks and stress state of lining is studied as well, which verified the effectiveness of the conclusions in the forepart of the paper. Research results can be referred for similar engineering.