Airport/Transit Award of Merit: Central Subway Tunnel
The first major subway project completed in San Francisco since the 1970s, the $241-million tunnels provide two miles of rapid transit from the southeast corner of the city to Chinatown, one of the country’s most densely populated neighborhoods and a thriving commercial district and tourist attraction. Completed in April, on time and on budget, the project required managing 450-ft radius curves, meeting stringent alignment tolerances and crossing 12 ft below active Bay Area Rapid Transit tunnels without service disruption. Five cross passages were built, along with a launch box under Fourth Street, a retrieval shaft and station headwalls. The toolbox of construction methods included tunnel boring machines with mono-block cutters, jet and compensation grouting, secant and tangent pile installation, slurry walls, cutter soil mixing and sequential excavation.