At 10.45am, on 7 October 2002, in Atlanta, Georgia, the first Robbins TBM broke through on the southbound drive of the $114M Chattahoochee tunnel in Cobb County.
Contractor Gilbert/Healy JV is constructing the 16.3km long, 5.3m i.d. tunnel, using two TBMs at depths between 39.5m and 115m.
The second Robbins TBM, which set off at the beginning of this year on the north drive, has about 1km to go. It is excavating through rock including gneiss, schist, quartzite and granite, between 140MPa-280MPa.
The tunnel is part of a scheme to meet new government standards of wastewater discharge, and will feed the RL Sutton reclamation facility near Chattahoochee River. It will also collect more stormwater during heavy periods of rain; providing enough extra storage to prevent sewage spills into the Chattahoochee river. The finished system is scheduled to come on-stream in October 2003.
The TBM will now be disassembled and moved to Atlanta for the $140M, 13km long Nancy Creek interceptor sewer. The Obayashi/CJB Contracting JV will operate the machine after emerging as the lowest of five bidders back in March of this year.
The Nancy Creek contract also includes: three construction shafts; eight vortex intake structures; and about 914m of smaller connecting tunnels. (See T&TI, February and May 2002.)
