Engineers finished boring the North drive of the Chattahoochee tunnel, in Cobb County, USA, shortly before Christmas last year. The event sees boring completed on the whole project.
The refurbished 5.6m diameter Robbins TBM, after completing the 15.3km long tunnel, will now be backed up, and brought to the surface. It started boring in November 2001, and has completed its task on time and within the project budget.
The Gilbert/Healy JV has constructed the US$113M tunnel for client Cobb County Water System, as part of a wastewater scheme that will feed the RL Sutton reclamation facility near the Chattahoochee river.
Two Robbins TBMs were used on the project, boring through gneiss, schist, quartzite and granite between 140MPa and 280MPa. The first TBM broke through on the southbound drive in October 2002.
Seventy per cent of the tunnel will now be lined with concrete, and the system should come on-stream in October this year.
