The high-speed railway between Beijing and Zhangjiakou in China that is a very famous project all around the world is now under construction. Badaling station is at the middle of this railway line and is designed as an underground station. The transition zone between the running tunnel to Zhangjiakou direction and Badaling station has a large span cross section with a dimension of up to 30 meters. Meanwhile, this large cross section also goes through the fault fracture zone. As a result, the supporting scheme and stability of the surrounding rock as well as seismic safety are the main concern about this major project. In this paper a 3-D rock-tunnel dynamic interaction finite element modeling is carried out to analyze the construction stage and seismic performance of the large span tunnel cross section. Numerical results have demonstrated the rationality of support system and revealed the seismic performance of the large span cross section.
The new Badaling Tunnel is located between Changping Nankou Town and Badaling Town in Yanqing County. The world's deepest and largest high-speed train station (Badaling underground station) which will be an important part of the 12km long tunnel between Beijing and Zhangjiakou will be 102m deep with a floor area of about 36000 m2. Starting section of the transition section of the station in Beijing directions is DK67+653 and that in Zhangjiakou direction is DK68+285. This tunnel station comprises of three different sized cross sections namely: small distance spaced section, large-span and triple arch section. The transition zone towards Zhangjiakou direction spans through a fault fracture zone which makes it vulnerable to seismic activity and needs to be investigated. Figure 1 shows the plan of the station.
Based on the prevailing geological conditions, seismic effects and station structure details form the comprehensive geological survey report, it is necessary to analyze the overall seismic performance of the Badaling underground station. The transition tunnel is of a maximum net width and height about 30.83m and 17.57m, respectively, with a height - span ratio of 0.57. The Zhangjiakou direction transition section passes through a fault fracture zone and is the focus of this investigation. The plan of this transition section is shown in figure 2. The surrounding rock is graded 3–5 and the Norwegian method is adopted for the excavation. Initial support system against the rock includes shotcrete, prestressed cables and prestressed anchors.