Construction Method Of Composite Stratigraphic Section Of The Tunnel Dynamic Segment

Taking Liuyanghe tunnel on Wuhan-Guangzhou passenger dedicated line as background, in view its characteristics that shallow buried depth,large span,complexity geological condition,high construction risk,tight schedule and so on, and according to the actual regular layered soils and the portal of tunnel located in foundation pit which make entering tunnel diffichult by double side drift method, but easy from crown, dynamic subsection method which enter tunnel from crown was advanced, and then, its theoretical basis,mechanical characteristic,key points of construction and measurement technicque were discussed concretely and systematically. The main achievements and innovative points were abtained as following:( 1 ) A new construction method named dynamic subsection construction method, which suitable for regular layed soils and sections which is difficult for entering tunnel from side wall, was advanced firstly, its core content is: diveding the upper bench to two parts as left and right, and then, changing the mid-partition from curve wall to straight wall, and the temporary invert and mid-partition of middle bench can be set additionally based on the in-situ geological condition. By this method, the disturbance among every construction step is small, operation simple, safety and reliable, and favorable to construct by mid or large machines, so the fast and convenient transform of tunnel construction methods in unhomogeneous formations comes ture, and the engineering quantity of temporary support was reduced, that is the engineering investment was declined.(2 ) Based on the force characteristic of large span tunnel in weak surrounding rock, the mechanical principle of dynamic subsection methed was discussed combineding with theory of axis change, its rationality and reliability was testified by theory, also the corresponding construction technique and operation key points were advanced.(3 ) By means of large scal business computer software, the plane and space numerical models of dynamic subsection construction method were put forward, the mechanic characteristics of support structure and physical field of surrounding rock in every construction step were analyzed concretely, through that, the mechanic characteristic and spatial effects of this construction method were revealed, and the force change mechanism of temporary mid partition and mid rock pile were emphatically elaborated, and its key sonstruction step and weak position of tunnel were obtained, at last, suggestions of construction and measurement were proposed.(4) Numerical models of construction methods (CRD,CD and Double side drift method) in common use for similar geological condition were put forward, their mechanical characteristics were analyzed concretely, and the compatative research between them and the dynamic subsection construction method were performed, so that excellence of dynamic subsection construction method was obtained by numerical explanation.( 5) Based on the test contents and method of existed normal tunnel, the measurement technique and management system of dynamic subsection construction method were proposed combineding with the former computed results, which applied in Liuyanghe tunnel.On 12th, Sep. in 2008, Liuyanghe tunnel on Wuhan-Guangzhou passenger dedicated line completed, which indicated that dynamic subsection construction method was reasonable, its ecnomial and social effects were notable. It obuvious that this method opened up a new construction method for tunnel with large span,regular layed soil and viarable geological condition, which has great engineering significance and reference value.