A Robbins TBM broke through in record time on July 11 at the Indianapolis Deep Rock Tunnel Connector (DRTC) project. The speedy machine not only completed a project with positive environmental impact, but also set three world records in the process.
The project was put in place by Citizens Energy Group and the U.S. Environmental Protection Agency (EPA) to reduce sewer overflows in the city’s neighborhoods and tributaries along the White River. Tim Shutters, Construction Supervisor of Citizens Energy Group states “There were a couple of different ways that we approached solving this issue and the one we chose was the deep rock tunnel because it would cause less disturbance for the people of Indianapolis, and afforded us the ability to upsize to a 5.5-m (18-ft) diameter tunnel. We could store flows rather than convey them and upgrade the treatment facilities.”
The 6.2-m (20.2-ft) diameter Robbins Main Beam TBM, owned by Shea/Kiewit (SK) JV, was refurbished and redesigned for the job. Originally built in 1980, the TBM has previously been used on at least five other hard rock tunnels including New York City’s Second Avenue Subway. The additions for the DRTC included new 19-in. disc cutters, variable frequency drive (VFD) motors, a back-loading cutterhead, and a rescue chamber. The machine cut a 12.2-km (7.6-mile) tunnel through limestone and dolomite 76 m (250 ft) below the city. A Robbins continuous conveyor system that included a horizontal and vertical conveyor was used for muck removal.
The DRTC project was launched in 2013 and was a very streamlined job, according to many of the workers. Multiple world records in the 6 to 7 m (20 to 23 ft) diameter range were broken on the job, including “Most Feet Mined in One Day” (124.9 m/409.8 ft), “Most Feet Mined in One Week” (515.1 m/1,690 ft), and “Most Feet Mined in One Month” (1,754 m/5,755 ft). “It couldn’t have been done without the guys in the tunnel working so well together while still keeping safe,” said Shea-Kiewit Project Manager Stuart Lipofsky, who is very proud of the machine’s records. Shutters was also blown away by the rates, stating: “SK rebuilt the machine into a hot-rod; they built a machine that was over-engineered for the rock.” Shutters, among many others, believes that the machine’s robust rebuild is responsible for the impressive rates and early breakthrough.
Although the project was ahead of schedule and broke records, one major challenge was encountered: groundwater inflow that was beyond what was originally anticipated. Near the mid-point of the tunnel, heavier-than-expected ground water inflows caused a slowdown in production. For the remainder of the project, much of the tunnel contained a few inches of water. This led to decreased production rates due to safety precautions and water clean-up. Lipofsky stated, “There are always challenges, and I would say our biggest issue here was dealing with ground water. We overcame it with a good pre-excavation grouting plan.”
Now that the main tunnel of the DRTC is complete, the project is moving into its next phase, which includes constructing a 5.5-m (18-ft) diameter cast-in-place concrete liner. The remainder of Citizens Energy Group’s overall tunnel system includes boring a network of four additional tunnels totaling over 27 km (17 miles) to reduce the wastewater overflow into the White River, Fall Creek, Pogues Run and Pleasant Run waterways. Solicitation for the next two tunnel phases is anticipated to occur in mid-2016. Based on the terms of Indianapolis’ Federal Consent Decree, the entire tunnel system must achieve full operation by the end of 2025.