On Nov. 27, 2012 a 20.2-ft diameter Robbins hard rock cutterhead arrived in Indianapolis. The arrival at the staging site was timed with a ceremony that included the city’s mayor and local officials, marking the assembly progress of the large Main Beam TBM. Once launched from a 250-ft deep shaft, the machine will embark on a 7.5-mile long wastewater tunnel for the Shea/Kiewit JV.
The contractor-owned Robbins machine was refurbished and redesigned in Cleveland, Ohio, and Mt. Pleasant, Pa., facilities following its most recent excavation at New York City’s Second Avenue Subway.
Its latest rebuild was complex, according to Dave Girard, Senior Engineer for J.F. Shea Construction: “We retrofitted a machine built in 1976 with the latest technology – in particular, variable frequency drive motors.” Other new components include the back-loading cutterhead with 19-in. disc cutters and rescue chamber.
Despite the complexities of the redesign, the machine is scheduled to be launched from a deep shaft in early 2013, proceeding toward the Belmont Wastewater Treatment Plant in what is expected to be competent limestone and dolomite rock. Robbins continuous conveyors, including a horizontal and vertical conveyor, will aid in muck removal on the long drive.
Once complete, the tunnel will be lined with unreinforced concrete, making the finished diameter 18 ft. Cleaner water is the ultimate goal of the city’s new Deep Rock Tunnel Connector (DRTC), along with four shorter tunnels that will be added on afterward. The DRTC will convey up to 550 million gallons of combined sewer overflows daily to the Southport Advanced Water Treatment Plant. By 2025, the network of five tunnels will total over 25 miles, and will reduce wastewater overflow into the White River, Fall Creek, Pogues Run and Pleasant Run waterways by 95 percent or more.