Bored tunneling for Singapore metro

This paper describes the planning, layout, and implementation of the Singapore Metro mass-transit system, emphasizing the criticality of the 22.4 km of bored tunneling required in the central area of the city. The original nine-year construction schedule and the subsequent seven-year accelerated program that was adopted are discussed, as are the extent of the tunneling works and the limited construction period of 3-1/3 years. The contractual arrangements for carrying out the works are outlined. The opportunity afforded by this concentration of soft-ground tunneling activity to compare performance in 38 tunnel drives, all of which excavated almost simultaneously in widely varying geological conditions, is considered unique. Factual details are provided covering the geological conditions along the tunnel drives, the contract packages, the tunnel profile, the tunneling methods, compressed-air equipment and procedures, spoil-handling equipment, temporary and permanent support, and water-sealing techniques. Settlements are reviewed, and tunneling performance for each drive is detailed. Some general conclusions are drawn from the owner’s viewpoint to assist in ensuring the timely and efficient completion of tunneled works in a complex transportation project.