Design and Rapid Construction Technique for Bibanpo High-speed Railway Bifurcation Tunnel

In China, the construction of high-speed railway infrastructure plays a more and more important role in promoting economic growth. However, because of its large turning radius and incapability in bypassing and avoiding, the length of development line cannot meet the needs of separating tunnel, which has driven high-speed railway tunnel bifurcation structure become a necessity in regions with steep high mountains, gorges, ridges and valleys. In the big excavation area of bifurcation transition section, long construction period and collapse of the surrounding rock often happen. To solve those problems, we proposed a new method with rapid holing through procedure and pre-stressed anchor cable support. The methods go as follows. We put forward an optimized process of excavating and breaking through one side of the tunnel first and drilling back through the other side in consideration of the large excavation area and long construction period. We presented reinforced support system of pre-stressed anchor cable in view of problems including surrounding rocks with no secondary lining, unstable structure and unbalanced load releasing. The system has been applied to Bibanpo tunnel, a project in Shanghai-Kunming high-speed railway. By using this method, all difficulties during construction have been broken through, The study could be used as a valuable example for bifurcation structure construction in urban arterial roads and high-speed railway tunnel with the similar geological conditions such as Chengdu-Kunming high-speed railway, Chongqing-Kunming high-speed railway, and Chongqing-Changsha high-speed railway which are going to be constructed.