Study On Stability Bearing Mechanism And Key Technologies Of Assembly Confined Concrete Support For Large Section Tunnel

With the rapid development of China’s economy and the increase of traffic demand,the construction of large cross-section tunnel has become a new normal.The combined support method of bolt-mesh-shotcrete and profiled steel arch is widely used in large-section tunnels.Due to the obvious different mechanical behavior between large-section tunnels and conventional tunnels in surrounding rock stress and deformation,the following typical problems occur in large-section tunnels:①low stiffness of initial support arch,insufficient longitudinal restraint and spray layer cracking results in partial bending and torsion instability of arch and then overall tilting,which can not give full play to its material strength;②due to the overall destruction of the initial support system,the spray layer cracks and falls,which leads to weak links in the support system,large-scale damage and even collapse;③workers work in the above dangerous environment leads to high safety costs,often resulting in low construction efficiency,frequent casualties,surrounding rock can not be effectively controlled.In view of the above problems,based on the basic characteristics of typical engineering problems of large cross-section tunnels,this paper studies the occurrence mechanism of various engineering problems,and puts forward an effective supporting method and construction technology:assembled confiined concrete support system,focusing on the parameters design of confined concrete arch joints and the spatial layout of arches.Parameter design and bearing characteristics of initial support structure were studied,key technologies of mechanized construction method was developed,and field mechanized construction technology of assembled confined concrete support system was formed.The main research work and achievements are as follows:(1)Typical engineering problems and occurrence mechanism of large cross-section tunnelCombining with field engineering practice,on the basis of sufficient field investigation and analysis,this paper sums up the damage forms and occurrence characteristics of several typical engineering problems of large cross-section tunnel at present,analyses the inducing factors of large cross-section tunnel engineering problems,and classifies them according to their main characteristics and mechanical mechanism.Based on the analysis of the mechanism of various engineering problems,the support concept of "high strength,high rigidity and integrity" and the construction concept of "safety,efficiency and economy" are put forward,and the assembly confined concrete support system is established.(2)Bearing mechanism of confined concrete jointsThe theoretical analysis and indoor mechanical properties tests of basic confined concrete members,tubular joints and assembled joints under pure bending and compression bending were carried out and the typical failure modes and mechanical characteristics of various joint members were defined;The simplified calculation models of two kinds of joints are established,and the strength bearing criteria of the joints are deduced,and the calculation methods of the bearing capacity of the two kinds of joints are formed.(3)Analysis of the stability bearing mechanism and spatial influencing law of confined concrete composite archBased on the static equilibrium method,the equilibrium equation,geometric equation and physical equation of multi-center confined concrete arch under out-of-plane instability are deduced,and the calculation method of critical bearing capacity of multi-center confined concrete arch is obtained;The out-of-plane stability of multi-center restrained concrete arch and arch spatial composite support system is studied.The influence mechanism of spatial layout parameters of restrained concrete support system such as arch spacing,arch stiffness,longitudinal connection ring spacing and longitudinal connection strength on the bearing capacity of arch is clarified,and the spatial layout parameters of arch are established.Number design basis.(4)Contrast test of stable bearing capacity of confined concrete composite archThe mechanical properties test system of composite arch in underground engineering was developed.The mechanical properties comparison test of restrained concrete composite arch and traditional I-shaped steel composite arch was systematically carried out.Through the analysis of ultimate load and mechanical deformation of composite arch,the law of mechanical deformation and instability of two types of composite arch were deeply studied.The failure modes clarify the stable bearing capacity and deformation failure mechanism of the two types of arch frames under the combined state.(5)Bearing mechanism of confined concrete support structureThe pure bending test of restrained concrete shotcrete composite support structure was carried out.The mechanical properties and deformation failure characteristics of restrained concrete shotcrete composite support structure were analyzed from the aspects of deformation failure pattern,load-displacement curve and ultimate bearing capacity.The characteristics of the overall bearing capacity of support system with different confined concrete arch forms and reinforcement mesh layout schemes were defined.The influence mechanism;Combining with numerical simulation,considering the strength of different concrete shotcrete layer,the spacing of different confined concrete composite arch,the ring spacing of different longitudinal connections and other factors,different calculation conditions are set up to study the bearing capacity characteristics of confined concrete support and the control effect of surrounding rock.(6)Research and Application of Key Technologies in Mechanized Construction of Large Section TunnelsAiming at the problems of low efficiency and poor safety of manual construction in the process of arch erection of large cross-section tunnel,the intelligent installation machine of arch frame,assembly type joint,longitudinal positioning connection and other assembly type arch supporting devices are developed,and the matching technology of mechanized construction is formed;The mechanical analysis of the whole construction process of the assembled arch frame is carried out,and the variation law of stress and deformation of each section in the whole lifting process of the arch frame is studied,and the stress mechanism of the arch frame in the whole lifting process is clarified;Field application of mechanized construction of assembled arch frame has been carried out,and construction efficiency and safety have been significantly improved.