PUTTING TAIPEI'S MAIN RAIL TUNNELS UNDERGROUND [IE MAIN LINE RAILWAYS UNDERGROUND]

This article describes the planning and construction of the Panchiao Extension Project (PEP), which is the third and most ambitious stage of an extensive programme to put the main line railways below ground in Taipei, the capital of Taiwan. The PEP originally put underground the main Taipei station and the existing main lines and railway yards, but it was extended to continue beyond Taipei's perimeter. It now comprises: (1) 9km of land and river tunnels; (2) two new underground stations; (3) one reconstructed at-grade station; (4) elevated and at-grade arterial roads; and (5) a new 15ha coach yard and maintenance facility. The rail tunnels will consist of adjacent, parallel concrete boxes, separated by a slurry wall that is part of the excavation support system. Each tunnel has 10.5 x 6.6m internal dimensions. The most significant project element is the new Panchiao underground station, planned as a transport hub for easy intermodal transfers. The tunnels are in a seismic area, with ground that includes soft silty clays and fine silty sands. To maintain railway safety and ensure the stability of buildings, there was an extensive monitoring and instrumentation programme.