Three tunneling world records have been beaten by the 6.2m diameter Robbins TBM that has completed the Deep Rock Tunnel Connector (DRTC) Project in Indianapolis, Indiana.
The Robbins main beam TBM, owned by Shea/Kiewit (SK) JV, was refurbished and redesigned for the job DRTC project was launched in 2013. While working on the 12.2km long CSO tunnel drive and towards the final breakthrough on Friday, 11 July 2014, the machine bettered three world records in the 6m to 7m diameter range.
“This could not have been achieved without the guys in the tunnel working so well together while still keeping safe,” said Shea-Kiewit Project Manager Stuart Lipofsky.
Proud of the machine’s records and impressed also with the rates, Tim Shutters, Construction Supervisor of client organization, Citizens Energy Group, said “SK rebuilt the machine into a hot-rod. They built a machine that was over-engineered for the rock.” As well as many others, he believes that the machine’s robust rebuild was responsible for the impressive rates and early breakthrough. A Robbins continuous conveyor installation, including a vertical conveyor and stacker, was also an important contributor to achieving the record-breaking advance.
Originally built in 1980, the TBM was previously used on at least five earlier hard rock tunnels including New York City’s Second Avenue Subway. The additions for the DRTC included new 19in disc cutters, variable frequency drive (VFD) motors, a back-loading cutterhead, and a rescue chamber. The machine excavated the 12.2km long tunnel through limestone and dolomite and up to 76m below the city streets.
The project is being built by the Citizens Energy Group to comply with US Environmental Protection Agency (EPA) regulations to reduce combined stormwater and wastewater overflows into the city’s tributaries along the White River. Shutters, for the owner, explained that “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 5.5m i.d. tunnel to store flows, rather than convey them, and to upgrade the treatment facilities.”
Although the project was ahead of schedule and broke records, one major challenge was encountered. Groundwater inflow was beyond that originally anticipated and near the drive’s mid-point, heavier than expected groundwater inflows caused a slowdown in production 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.” During the celebrations the tunnelling crews remembered a team-mate who was injured fatally during his shift.
Now that the main tunnel of the DRTC is complete, the project is moving into its next phase, which includes constructing a 5.5m i.d. in-situ concrete liner. The overall CSO control program by Citizens Energy Group includes a network of four additional tunnels for a total of more than 27km to reduce the wastewater overflows 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 the Indianapolis Federal Consent Decree, the entire tunnel system must achieve full operation by the end of 2025.