The Robbins Company has won the contract to provide the TBMs on the Nancy Creek sewer project in Atlanta, USA.

The Nancy Creek Contractors, a joint venture between Obayashi Corporation and CJB Contracting Inc, will use two hard rock machines to bore the 5.6m diameter, 13.3km long tunnel through predominantly very fine-grained medium grade metamorphic rock.

The Robbins TBMs will have 2,200kW (3,000 hp) of cutterhead power, and will be fitted with two roof drills that can be rotated into probing positions for ground investigations and grouting ahead of excavation. For rapid ring erection and full ring steel support, the TBMs will have a ring beam erector. The backup systems will pull the continuous conveyor belt that will remove muck from the tunnel.

The Nancy Creek Contractors won the contract in March this year, with a bid of $138M, which will also include three construction shafts, eight vortex intake structures, and about 914m of smaller connecting tunnels.

The sewer is designed to prevent sanitary sewer overflows into the waterways, and the completion date of 31 August 2005 is enforced by a court mandate. Fines will be levied if this date is missed, encouraging the contractors to work 24 hours a day, seven days a week. A third TBM may be introduced.

Robbins provided similar machines to the Chattahoochee project, not far from Nancy Creek. The TBMs should have completed 14km (out of 15.2km) by the end of the year.