Robbins TBM Breaks Through Nancy Creek Tunnel - us/60A Robbins TBM has broken through on 27th September to a construction shaft, thus connecting the two sections of the 13 km Nancy Creek sewer tunnel in Atlanta. The machine cut a 5.6 m-diameter tunnel through the bedrock and broke through near the tunnel's midpoint, ending its 8 km portion and connecting the two legs.During heavy rains, raw sewage leaks from the decrepit sewer system, flowing into basements, creeks and ultimately into the Chattahoochee River. The Nancy Creek tunnel will carry sewage from DeKalb County beyond the city's northern limits, flowing southwest across Atlanta like Nancy Creek to a treatment plant near the Chattahoochee River. It begins under Johnson Ferry Road just south of I-285, then travels southwest under Buckhead to the grounds of the R.M. Clayton Water Reclamation Center in northwest Atlanta. The tunnel was carved simultaneously by two refurbished Robbins TBMs, which previously bored the 15.3 km Chattahoochee tunnel in Cobb County, Georgia. They were lowered into the ground through two vertical shafts. One drilled 5,020 m from Roswell Road to Johnson Ferry Road shaft site. It broke through in May 2004. The other just finished its 7,995 m on 27th September from R.M. Clayton to the Buckhead shaft site at Roswell Road. Construction on the Nancy Creek tunnel was begun on 2nd July, 2003 with the first of two TBMs. Nancy Creek Contractors, a joint venture between Obayashi and CJB Contracting, bored through hard metamorphic rock of gneiss, schist and quartzite, with some granite.The scheme is expected to cost USD131.5 million by the time it is completed in December 2005. Before the tunnel can be used, its interior must be lined with a 30 cm-thick ring of concrete. Meanwhile, a pumping station must be built at the R.M. Clayton site, and the existing treatment plant there must be expanded. The sewage will be stored in the tunnel until it can be lifted to the plant, where it will be treated, then poured into the Chattahoochee. Subscribe to E-News Weekly 46/2003 & 42/2002. Visit www.robbinstbm.com and www.cleanwateratlanta.org/NancyCreek 41/04.