Study On Schemes And Risk Analysis Of The Expanded Metro Station Under Shield Running Tunnel

In order to solve the contradiction of construction time limit for running tunnel constructed by shield method and station in domestic, and to seek for the breach of large-scale application for shield method in domestic subway engineering, a new-style station construction method has been brought forward in this paper based on large numbers of overseas project examples and domestic economy and technology level. The new-style station construction method is that the station will be constructed by shield method and tunneling method (or cut and cover method) under the condition of shield running tunnel. This is a very important and urgent research problem and has a wide application prospect.Surrounding the new-style station construction method, structural schemes and crucial construction technologies and model test and numerical simulation of station construction process and risk analysis have been researched roundly in this paper. The research methods include numerical simulation and model test and theoretical analysis and etc. The main work and the achievement are as follows:(1) Based on overseas literature information and advices of pertinent experts, structural design principle of the new-style station and seven conceptive structural forms have been conceived, and fit structural scheme for Beijing stratum conditions have been recommended. Crucial technologies which include the design principle and the assembled fashion and the assembled position of shield segments and also the connective node design of shield segment and structural main body have been discussed in detail. These study achievements insure that the structural schemes satisfy desired station function and code for design of building structure and domestic technology and economic level.(2) During the course of new-style station construction, the most crucial and the most especial and the most adverse step is dismantlement of partial shield segments, so the protection to the split ring segments decides the success or failure of the new-style station construction method. Based on the collection of relevant information about construction technics, A new support system which is made up of pile outside the shield tunnel and steel-tube column in the shield tunnel and prestress (for short PCPrSS), has been commended. And the scheme design and the technics of PCPrSS have been discussed in detail. (3) In virtue of 1:10 large-scale model test, detailed experimentation scheme has been designed and implemented for the construction process of pylon shaft station. The variational rules of strain on the shield segments and the prestressed tightwires and the transient steel tube supports, and at the same time the variational rules of convergence of shield segments and soil pressure and displacement around the station tunnel have been achieved accordingly. It has been proved that the construction scheme is feasible under the condition of model stratum.At the same time, by dint of FLAC^3D software, numerical simulation has been implemented for the construction process of pylon shaft station. As compared with the results of model test, the results of numerical simulation have showed the analogous qualitative rules. Therefore it is proved again that the new construction scheme is feasible.(4) By adopting many discriminating means, for example analogous engineering experience and study achievement of this paper and advice of pertinent experts, especial construction risks have identified and countermeasures to answer these risks have been also brought forward for the vertical shaft station and the pylon shaft station.