Study On The Selection And Mechanical Behavior Of Prefabricated Arch Open Hole Joint

Recent years have seen a wide application of prefabricated assembly structures in China’s construction industry for their efficiency,quality of components,environmental friendliness,and low repair costs.However,as regards to tunnel and underground engineering,apart from the shield tunnel lining structure using prefabricated components,the traditional cast-in-place method still holds the dominant position in the construction of large quantities of drilling and blasting method and open-cut tunnel lining,which is not only complex in procedures and low in efficiency,but also is prone to cracking,falling blocks,leakage,and settlement and other engineering quality problems and structural damage.That’s why the national scenarios,namely the national "double carbon" strategy and the "13th Five-Year Plan" for assembly and construction,have been set in place.In this thesis,based on the eight-lane tunnel project of Xinsen Avenue in Chongqing High-Tech Zone,the selection of joints and their mechanical behaviour of prefabricated arch-shaped open cavern structures were systematically studied through model tests and numerical simulations,with the following research results obtained.(1)According to domestic and international literature research and engineering investigation,combined with the characteristics of mountain highway tunnels,the optimal joint form of prefabricated arch tunnel structure was selected as follows,that is double tenon,plus bolt with external additional tension device joint or double tenon and bolt joint for the top of the arch,and reinforcement jointing and casting with reinforcement jointers for the side wall corners,proposing a two-part structural scheme for prefabricated arch tunnel and cast-in-place back arch scheme.(2)Three types of structural members,including cast-in-place reinforced concrete beams,double tenon and bolt joints and double tenon and bolt joints with external additional tension device,were subjected to 1:2 reduced scale axial bending loading tests to observe the damage process of the members in the tests and to draw the relationship curves of the two types of joints.The six stages are shown as follows: no cracks → cracks appear for the first time in the centreline area → the number of micro-cracks increases,spreads to the sides and develops diagonally upwards →cracks gradually connect and widen → cracks penetrate to the top surface of the structure → damage to the member.(3)The development of the maximum tension,concrete strain,vertical displacement,angle of rotation and flexural stiffness of the two joints under different combinations of axial bending was systematically investigated by using reduced scale axial bending loading tests and ABAQUS numerical simulation tests,the flexural stiffness of the joints was compared and analysed,and the empirical formulae for the flexural stiffness of the two joints were proposed for axial forces of 500 k N and 1000 k N respectively.(4)ABAQUS was used to establish a three-dimensional finite element model of the tunnel stratum-structure to study the force and deformation characteristics of the prefabricated arched open cavern structure under the action of the surrounding rock load;considering two factors,such as the burial depth of the tunnel and the surrounding rock grade,the overall mechanical performance of the lining of the assembled arched open cavern structure was analyzed,and the maximum principal stress,transverse displacement and vertical displacement of the lining of the assembled arched open cavern structure under different working conditions were investigated.and vertical displacement under different working conditions.This thesis proposes a structural solution for prefabricated arched open caverns and investigates the mechanical behaviour of prefabricated arched open cavern structures,providing theoretical reference and technical support for the realization of cut-and-cover tunnel lining assembly.