Research On Mechanism Of Tunnel Face Failure In Soft Surrounding Rock And Failure Control Measures

Recently,tunnel constructions are become more and more popular in many fields such as railway,expressway,and subway.The numbers and mileages of tunnels are growing rapidly.China is really a great power of tunnels.A great improvement in the construction technologies has been got.However comparing with those super powers,there are still large gaps to fill.The construction of tunnels faces much more daunting tasks.With the increase of tunnel construction,the problems existed in the construction of tunnel with soft surrounding rock are getting more and more tricky.The soft surrounding rocks which have poor engineering properties can be easily influenced by excavation disturbance which could lead to obvious deformation.Though many studies are focusing on the failure mechanism of soft surrounding rock and its control measures,there is yet no consensus.Explorations on the deformation rule of the soft surrounding rock tunnel,key influence factors,the stability of tunnel face,and the failure mechanism are still at the initial stage.In this thesis,based on vast literature and extensive practices,numerical simulation,theoretical analysis and monitoring measurement were adopted to carry systematic research on mechanism of tunnel face failure in soft surrounding rock and failure control measures.Lianyue tunnel project was chosen as the background to study the deformation characteristics of tunnel with the shallow buried soft surrounding rock by using monitoring measurement and numerical simulation.Stability factors of the tunnel face have been analyzed by study the extrusion replacement in the numerical analysis.According to the destruction process analysis for the tunnel face,failure mode of the turnel face were classified into two patterms,one is shallow buried failure mode when the surrounding rock of tunnel face cannot form a complete ellipsoid,the other is deeply buried failure mode when the surrounding rock of tunnel face can form a complete ellipsoid.Then the failure model of tunnel face has been established,the formula for calculating the instability of tunnel face has been put forward,four positional relationships between tunnel depth and height of slump ellipsoid has been studied based on silo theory,Terzaghi,s theory and drawing ellipsoid theory.The consistency of derivation formula and classic formula has been verified by using exanples.The calculated value by derivation formula is coincide with the result of numerical simulation.According to strength reduction theory,cusp catastrophe theory,and energy dissipation theory,a judging method for stability of txunnel face has been developed by using displacement saltation and plastic strain energy saltation as major criterions.The pre-reinforcement measures against instability have been categorized.The stability of tunnel face has been studied under different pre-reinforcement conditions by using safety factor as a criterion.Suggestions for pre-reinforcement have been given.At last,Pre-reinforcement measures which combined horizontal high pressure jet grouting and long pipe roof has been designed for layer by studying the stability of the face of Jiaheyuan underground passage,analyzing the pre-reinforcement effects according to the field monitoring results.