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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.


Location: San Francisco, California

Owner: San Francisco Municipal Transit Authority (SFMTA)

Engineer(s): Parsons Brinckerhoff Telamon JV

Construction Manager: McMillen Jacobs Associates

Partner(s): Impregilo S.p.A., S.A. Healy Company

Contract type: Fixed Lump Sum

Status: Completed


  • 2015 ENR California Award of Merit in Airport/Transit
  • 20.4-ft.-dia. twin tunnels
  • Soldier pile tremie concrete (SPTC) wall and launch box constructed beneath an I-80 overpass with limited overhead clearance restraints
  • 50-ft.-square by 50-ft.-deep permanent secant pile retrieval shaft
  • Four concrete slurry diaphragm walls for subway stations
  • Jet grouting ground improvements for tunnel breakout and station endwalls
  • Compensation grouting to prevent and control ground and structure settlement
  • SEM cross passage excavation for five cross passages, including one ground freeze

17, 200 LF of twin tunnel

>8 ft. of vertical clearance between existing tunnel infrastructure

450-ft. radius curves

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