Study On The Mechanical Characteristics Of The Lining For Super-large Sections Of The Loess Highway Tunnel

Now, the constructed and constructing highway tunnel with3or4lanes basicallybelongs to the loess highway tunnel with large cross section, which has distinct characteristicsand can effectively high-density traffic flow, it will be the mainstream of future tunnelstructure form. Concluded from geological condition, topographic condition and design data,followed difficulties will be occurred when large cross section of shallow-buried loesshighway tunnel is constructed: large excavation area, shallow tunnel depth, low strength ofsurrounding rock, complex tunnel force and construction procedure and so on. It is differentwith ordinary single shallow-buried loess highway tunnel with2lanes, and the amount oflarge cross section of shallow-buried loess highway tunnel is little, researches are little atdomestic and overseas, thus some problems are still unknown. The paper based on TangJiaTableland large cross section of loess highway tunnel of Xian-BaoJi reconstruction andextension engineering, the paper comprehensive applies field test, theoretical analysis andnumerical modeling to research mechanical property and deformation characteristic atprimary support and mechanical property of secondary lining of large cross section of loesshighway tunnel. The main works and results were as follows:(1)Surrounding rock deformation of highway tunnel with super-large cross section inloess has gone through three stages, which is first rapid deformation, second sustainablegrowth, third slow growth; The vault crown settlement is greater than horizontal convergencedisplacement, deformation of primary support mainly presented overall sink, suggested thatthe construction unit should adopt the double drift method to control overall sink;(2)Five theory methods, highway tunnel design specification, Xie Jiajie formula,Terzaghi theory, Pu.s theory and Bill bauman formula, are used to calculate the magnitude ofthe surrounding rock pressure respectively and compare with the measured value, Thecalculation result from Terzaghi theory is closest to the measure value, Proposed the Terzaghitheory of lateral pressure coefficient correction method in this foundation, the field test verify its feasibility, Terzaghi theory may become the recommended method to calculate thesurrounding rock pressure for super-large sectional loess tunnel,which is proved feasible bythe field research and provide reference and basis for the similar tunnel lining design in thefuture.(3)After analysis of surrounding rock pressure calculation method and field investigation,it was firstly found the relationship between ground surface cracks and buried depth, thepaper points out some problems with the exiting demarcation criterions of buried depth whenthey are used to loess highway tunnel, and puts forward the thought through changeregulation of soil lateral pressure coefficient in the center line, which is proved feasible by thefield research and provide reference and infer the Tang Jia Yuan tunnel buried depth range for90m.(4)By filed monitoring of surrounding rock pressure, the paper statistically analyzed thepressure, obtained the pressure distribution form of TangJia Tableland Tunnel: the maximumof vertical direction doesn’t occur at vault area, it occurs at nearly40°of axle wire, while therest is less than the vault, the horizontal pressure distribution is linear growth at arch area anduniform at straight wall.(5)By researching the security threshold of domestic and overseas loess tunnels, thepaper put forward the security threshold of TangJia Tableland Tunnel, based on “convergence–constraint” theory, computational simulation and comprehensive determination of ultimatedisplacement by data. By contrasting GM(1,1) of gray forecast model, residual error modeland information renewal model with tested data, information renewal model was chose as theprediction model of TangJia Tableland Tunnel, the paper raised a set of deformation warningstandard for large cross section of loess highway tunnel.(6)Combined with the existing specifications and the characteristics of large crosssection of loess highway tunnel, the paper respectively considered corresponding relationshipbetween surrounding rock severe and lateral pressure coefficient, established formula oncoefficient of elastic resistance K, calculated the stress of the secondary lining undermeasured load conditions with TongJiShuGuang design and analysis software for highwaytunnel and evaluated the safety of the secondary lining.