Optimization Of Badaling Single-arch Underground Station With Exceptionally Large Cross-section Of Beijing-Zhangjiakou Intercity Railway

The badaling underground station is the most important control project of the proposed new jing-zhang inter-city railway. This project will be the first construction in China to build a station in mountains and also few examples can be found over the world. Lacking of analogous projects as references is one of two most significant problems in the preliminary stage. In addition, the internal difficulties of this project, such as the deep foundation depth, large excavating area, complicated structures, also increase the uncertainty and ambiguity in selecting the final practical design from the proposed drafts.Taking badaling underground station as basis, my thesis focuses on modifying the design of the single arch structure with large span and super large cross section. FLAC3D method have been used to build the construting model and do the simulations. Results are summarized as follows:1) In the first chapter, current analogous projects both in China and other countries were summarized. Features and difficulties of this project were analyzed. This chapter presented useful information and references in selecting excavating and constructing methods for the construction of the badaling underground station;2) The basic theory of the mechanics of surrounding rock of tunnel and underground chamber were reviewed at the beginning of this chapter. In the light of this theory, mechanical characteristics of surrounding rocks were studied. Furthermore, I investigated all the important factors influencing the stability of the surround rocks. This chapter will be theoretical foundation for the construction and tunnel supporting of the badaling station.3) In this chapter, I evaluate the geological condition and the initial stress field in the area of the station. FLAC3D programs were used to simulate the full constructing process, using two different methods, Side-heading method and single-pillar method. A detailed study was conducted to learn effects of the excavation to the surroundings, such as the ground settlement, the surrounding displaced of the chamber and the size of plastic zone. According to our simulation and analytical results, the better constructing method was selected, which will be used in the next chapter.4) Taking left-right relative displacement, ground settlement and plastic zone as indicators, the orthogonal tests were used to optimize anchor spacing, anchor length, row spacing, and the thickness of the shotcrete. Through the Quadratic Regression Test, We found that the relative displacement of the top soleplate of the stations depends on the anchor length and the thickness of the shotcrete.In conclusion, our results provides direct guidance of the proposed badaling underground station, and gives insights in designing deep-buried large-span station and underground structures.