Central Subway Tunneling
Location: San Francisco, CA

Project Partner: Nicholson Construction Co.

Challenge: Settlement mitigation and compensation for a verity of mid- and high-rise buildings as well as BART & MUNI tunnels in downtown San Francisco during tunneling excavations underneath.

Overview: Condon-Johnson was contracted to install over 20,000 linear feet of sub-horizontal Manchette Tube System (TAM’s) in close proximity of sensitive structures such as existing BART and MUNI tunnels underneath Market Street Throughout this operation, CJA injected over 75,000 gallons of grout during pre-conditioning and active compensation grouting. CJA utilized advanced alignment tools and downhole survey methods to ensure drilling accuracy in vicinity of existing subsurface structures.

Results: By utilizing skilled workforces, advanced equipment, cutting-edge drilling, surveying, and grouting techniques, Condon-Johnson managed to successfully complete this grouting work, resulting in minimal settlement of existing structures due to tunneling activities as well as creating a controlled heave to balance any existing non-uniform settlements in targeted structures from before.