Research On The Key Technology For Design And Construction Of The Double-Arch Tunnel In The Soft Surrounding Rock

With the rapid development of highway in China from the nineties of the twentieth century, the method of neighborhood tunnel or the method of separate tunnel often is adopted because of the difficulty of highway line or other factors in the construction of highway at the Midwest. But the choice of the tunnel project is restricted not only by the topography, geological condition, but also by all kinds of indexes under the condition of the special geology and the topography.The excavation and the supporting of the double-arch tunnel is alternate to process, which makes the conversion complicate between the stress change of the surrounding rock and the supporting load because of the big span and the complicate structure in the double-arch tunnel. Some double-arch tunnels have been build in our country, but few effective and similar engineering has been used for reference at present and the design criteria of the tunnel design has not been established up to the present, especially the informational monitoring norm of the double-arch tunnel construction is searching and accumulating experiences. The double-arch tunnel has some disadvantages, such as, the time limit for tunnel is longer than other tunnels , working procedure is complicated, the cost is higher than other tunnels,ect. It is an important factor that the informational monitoring norm of the double-arch tunnel construction needs farther study except that the structural pattern of the double-arch tunnel is improved on.The load-structure method and the strata-structure method have been adopted from the enunciable papers in the calculating method of the double-arch tunnel structure design. It is important for load-structure method to make sure load because the supporting structure bears deformation pressure and does not bear relaxation pressure. It is unreasonable to adopt the computing method of single tunnel because of the difference between double-arch tunnel and separate tunnel in the span and the construction method. This paper puts forward deep or shallow burying norm of the double-arch tunnel and the calculating method of the surrounding rock pressure on the double-arch tunnel by analyzing the influence field of the tunnel balance arch in the construction.With the application and development of the double-arch tunnel, the cross-section pattern also develops rapidly. Studying on the influence factors and the classification of the cross-section pattern and the structural mechanics characteristic in the double-arch tunnel, the paper achieves that the cross-section pattern must require some conditions, such as the tunnel construction clearance, the tunnel ventilation, the road line, the tunnel waterproof-drainage, the engineering geological conditions and the structural mechanics etc. anyone factor influences probably the overall structural stability of the double-arch tunnel and the tunnel durability of the later use. The cross-section pattern of the double-arch tunnel is divided into the single-middle-wall tunnel and the separated-middle-wall tunnel by the middle-wall pattern by analyzing the cross-section pattern of the double-arch tunnel.As far as the construction method of the double-arch tunnel, this paper adopts a large similar model experiment and the FEM method to study the construction method of the double-arch tunnel in the soft weak surrounding rock. By contrasting and analyzing the surrounding rock displacement, the stress of the first lining, the transformation of the middle-wall and the vertical stress, this paper has established the reasonable construction method of the double-arch tunnel in the soft weak surrounding rock. At the same time according to the field monitoring measurement, this paper has an emphases on analyzing the structural mechanics characteristic and the tunnel clearance displacement about middle-tunnel-half-section and three-tunnel method.The middle-wall is the core component of the double-arch tunnel and it's structural mechanics characteristic is very complex, whose internal force need be adjusted in the whole structure of the double-arch tunnel. It is the position of the stress concentration in tunnel. At the same time the mechanics behavior and the displacement subside of the middle-wall relate directly the whole stability of the double-arch tunnel. The mechanics behavior of the middle-wall has been researched by the model test, the field monitoring measurement and the finite element numerical analysis, which come to conclusion that the mechanics behavior of the middle-wall relates with the construction working procedure, the construction method, the excavation section space, the supporting type ect, and the reasonable distance between the excavation section of tunnels in the double-archtunnel has been set up. The reasonable excavation distance should be the double span of single tunnel for the double-arch tunnel in the soft surrounding rock, and the time limit for the tunnel construction do not less than 15 days during the double span of single tunnel in order to release steadily for the surrounding rock stressing.The informational monitoring norm of the double-arch tunnel has been analyzed by the field survey measuring and the large similar model test and the finite element numerical analysis. The security control norm of the surrounding rock displacement has been researched deeply and set up the control norm of the clearance displacement and the vault subside in the soft surrounding rock of the double-arch tunnel, at the same time the management measuring norm of the field construction on the double-arch tunnel has put forward.which make the double-arch tunnel design develop from the qualitative design or experiential design to the qualitative design and the quantitative design. Research on the minitoring norm for the information of the double-arch tunnel not only offer effectively safeguard measure to constructed safely in tunnel engineering but also revises the supporting parameter and optimizes the construction mechanics characteristic of the tunnel supporting.Because results acquired in the dissertation by means of numerical simulation and test are basically consistent with the results by spot measuring , analysis theory and method concerned in the dissertation is reasonable. Thus theoretical basis and guidance are provided to real engineering, at the same time, a series of key techniques and problems are solved. Valuable design, construction and scientific research experience is accumulated and provided to similar engineering.