Study On The Design Method Of Double-shielded TBM Segment Structure In The Squeezing Ground Under High In-situ Stress

Currently,Double-shielded TBM is more and more widely applied in water diversion tunnel,railway tunnel,roadway tunnel,municipal tunnel and subway tunnel all over the world.But the squeezing deformation of surrounding rock under high in-situ stress is quite common in the tunnels excavated with Double-shielded TBMs,and gradually become a big problem in project constructions.Some engineering cases have shown that the squeezing deformation of surrounding rock is one of the main causes of the break of double-shielded TBM segment structure.Based on the analysis of the characters of the deformation and failure of the surrounding rock in double-shielded TBM tunnel in squeezing ground,this thesis has established the calculation method for deformation pressure of double-shielded TBM segment in squeezing ground;then the calculation model for certain segment structure is established in the consideration of the characters of double-shielded TBM in squeezing ground;finally,the design method of double-shielded TBM segment structure in squeezing ground are put forward.It is concluded that:(1)According to research,in the consideration of the characters of double-shielded TBM constructing and supporting in squeezing ground,this thesis has revealed the character of the excavation and unload process of double-shielded TBM in squeezing ground.In this process,the surrounding rock undergoes 3-phases deformation release:? pre-deformation release;?the deformation release in the area of shield;?the deformation release in the process of coordinating to stable between segment,backfilling player and surrounding rock.Meanwhile,the character of transverse failure of surrounding rock in tunnel is revealed:the surrounding rock in the arch of the tunnel is easy to come loose and drop off,the backfilling layer is week in transferring the pressure of surrounding rock,the ground resistance coefficient in the arch of the tunnel is heavily lost.(2)On the basis of the character of excavation and unload of surrounding rock in the excavation process of double-shielded TBM,this thesis has established the calculation method for deformation pressure of double-shielded TBM segment in squeezing ground which has taken the excavating time into account.What's more,the combination support rigidity formulation of segment and pea gravel backfilling is put forward and the mechanical function of pea gravel backfilling player is discussed deeply.(3)Based on the support characteristics of double-shielded TBM in squeezing ground,this thesis has established the calculation method for pea gravel and ground resistance coefficient;ascertained the approximate quadratic relation between rotating stiffness of joint and the thickness of segment and based on it this thesis has established the calculation method of stiffness of joint.Then the calculation model for double-shielded TBM segment structure in squeezing ground is established.(4)Based on the study on affection laws of the thickness of segment and reinforcement on crack width of segment,this thesis has established the design method for segment;based on the mechanical character of no-liner segment joint,the design method for the size,material and anchorage length of joint bolt is put forward.