| In recent years, the development of transport in China has led to the rapid emergence of rail transportation. With a large number of subways and high-speed rails having been built, the construction of the tunnel gradually becomes one of the important parts. New Austrian Tunneling Method has been used widespread by the tunneling workers due to its advanced consideration, which is the Theory of the Surrounding Rock Weight. Taking into account of the condition of weak surrounding rock and basing on the New Austrian Tunneling Method, construction by step method has been used by others for its unique advantages of bearing load by itself. The most important thing is to think about the safety and efficiency when studying a construction method. This paper is mainly to analyze the support measures and the construction phases, etc in the step construction method through the ground deformation caused by the tunneling construction.The background of this paper is Fouling Tunnel weak surrounding rock;First and for most, according to the actual tunnel construction and the geological conditions, using the MIDAS/the GTS finite element software to establish a data model, including three stages:up’ring excavation, core soil excavation and under step excavation, this can simulate numerically the process of the excavation with step method, with two-meter drilling depth. Through the methods of tunnel vertical displacement, horizontal displacement, the stress characteristics of surrounding rock, the shape of the plastic zone and the law of development, etc of the construction, this paper aim to reveal the influence to the deformation caused by the different tunneling phases. However, when the drilling depth becomes two meters, the safety circumscription would be in danger. And it is necessary to shorten the footage in face of a higher geological circumstance. Therefore, it is frequent to adopt one-meter footage contrasting with two-meter footage in the engineering simulation whose security reserve (margin) is more adequate. It can not only provide a scientific basis for the future constructing, but also demonstrate the "short footage" constructional principle of the New Austrian Tunneling Method.Secondly, in the actual project monitoring measurement, the greatest difference between the subway tunnel and mountain tunnel is that the subway tunnels are mainly reflected in surface subsidence while the mountain tunnels are performed by the subsidence of the cave dome and the horizontal convergence. The reason is that the burial depth of the mountain tunnel is too deep to be measured, so that the upper part of the mountain surface subsidence is unpredictable. Fouling Tunnel engages in identifying the most influential constructing phase mainly through analyzing the vault settlement and the horizontal convergence of the three phases. Moreover, it can determine the cause of the deformation and find out the appropriate response measures.Finally, comparing the values of the numerical simulation and the values of the actual monitor measurement and analyzing the similarities of them through the overall trend of the deformation, this aims to demonstrate the reasons of the ground deformation caused by the construction with step method and find out the corresponding appropriate solutions.Theory derived in this paper provides a great amount of guidance and technical basis for the construction of the Fouling Tunnel. At the same time, it can also provide reliable references to the similar situations, like the weak surrounding and construction with step method. Meanwhile, it is of great significance for ensuring the safe constructions and scientific guidance the constructions similar with the weak surrounding conditions. |
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