As part of the first major subway project completed in San Francisco since the 1970s, Barnard Impregilo Healy JV constructed two miles of tunnel from the southeast corner of the city to Chinatown, one of the country’s most densely populated neighborhoods and a bustling commercial district.

In an effort to improve access to Chinatown, SFMTA expanded the city’s Third Street Light Rail to include subway travel. The Central Subway Tunnel Project within this program extended the existing Third Street Light Rail T-Line with precast segmentally-lined twin tunnels. To bore the tunnels, two EPB TMBs passed through a variety of ground conditions ranging from soft ground to clays to hard rock formations. The team also constructed four cross passages, a launch box under Fourth Street, a retrieval shaft, and station headwalls. Despite significant challenges, including managing tight radius curves, meeting stringent alignment tolerances, and crossing below active BART tunnels without disrupting service, the project finished on time and on budget.