Indy's Deep Rock Tunnel project progressing.
The Deep Rock Tunnel Connector project will include a 25-mile-long deep tunnel system, 18 feet in diameter with a storage capacity of 250 million gallons and will significantly reduce the frequency and amount of raw sewage overflows during rains.
Raw sewage captured will be stored in the tunnel and then transported to the wastewater treatment plant. The enhanced tunnel will have the capacity to store raw sewage during large storm events. All sewage transported and stored underground in the tunnel system is sewage that otherwise could have gone directly into the area's waterways.
Currently, when as little as a quarter inch of rain falls, combined sewers reach capacity and raw sewage overflows into local rivers and streams.
The project is being constructed for Citizens Water, a division of Citizens Energy Group (Citizens). Construction of the $179.3 million project is a joint venture of J.F. Shea, Los Angeles, CA, and the Kiewit Corp., Omaha, NE. Shea-Kiewit has considerable experience with deep tunnel projects.
The first phase of the project is an eight-mile-long tunnel, said John Morgan, manager of Citizens Energy special projects group and manager of construction.
"This project is the backbone of our deep tunnel storage system," said Morgan. "Its construction creates the mechanism for the transfer of flow from our entire deep tunnel system. Additionally, it allows for collection of three combined sewer overflows, two of them being 'worst offenders' in our system."
The tunnel system is being built in bedrock below the city using a specialized tunnel boring machine. After the machine bores the tunnel, a concrete tunnel lining will be installed to help keep groundwater out and keep sewage in the tunnel.
Information about the project has emphasized that deep tunnel technology reduces disturbances to neighborhoods along the project route during construction. Because the tunnel is being constructed below groundwater levels, impact to area wells, gas and electrical lines, existing sewers and other utilities will be significantly reduced. Traffic disruptions and property easements needed to construct the project also will be minimized.
Preliminary work and site preparation began in late 2011. Excavation of the tunnel is expected to begin in January 2013.
By mid-year 2012, Morgan said Shea-Kiewit joint venture crews were excavating at the launch shaft location. Spoil has been removed, but rock from 100 to 283 feet below the ground surface must be removed, and a chamber large enough to accommodate the tunnel boring machine (TBM) must be opened. Installation of the slurry walls also is under way.
The tunnel will be dug by a massive Robbins 203-205 TBM tunnel boring machine (TMB) that will be approximately 350-feet long with trailing gear and weighs approximately 900,000 pounds. The machine produces 2.9 million pounds of thrust. Its cutting head will be 20-feet, 2-inches in diameter.
The TBM came out of the ground last fall after completing a subway tunnel in New York City and currently is being rebuilt for the Indianapolis project in Mount Pleasant, PA. Nearly 75 semi-trailer truck loads will be required to get the machine to the Indianapolis project site. Delivery of the TBM is expected in September.
Once excavation of the tunnel begins, it is expected the machine will excavate approximately 100 feet per 24 hours--actual production rates won't be known until construction is under way.
A conveyor system will remove muck from the tunnel to the surface for hauling to an offsite location. It is estimated that approximately 1 million cubic yards of material will be removed from the tunnel during the project with as much as possible reclaimed for reuse.
Grippers will extend from the tunnel rib and propel the machine as it slides along the tunnel invert. The trailing gear runs on rails. Morgan said the trailing provides the TBM's means of production, including hydraulic equipment, power transfer, steering, rock bolts, strapping and various mechanical materials.
Alignment of the tunnel will be maintained by a PPS guidance system which automatically determines the exact position and driving direction of the TBM in three dimensional space and provides the operator with information necessary to keep the machine on course.
The tunnel will be braced when necessary as the machine moves forward, Morgan continued. It is expected the lining will begin when the TBM has advanced beyond the first utility shaft location, a distance of about 5,000 feet from the launch. The lining will be clear concrete, not containing rebar. The specified strength is 6,000 psi and will be installed via use of slip forms.
Because the launch shaft is located within a flood plain, Morgan said a part of the project is to extend an existing levee to protect the project site and pump station to be constructed later.
Currently, approximately 50 workers are on site.
The Deep Rock Tunnel Connector, scheduled for completion in 2017, will transport wastewater from four other connector tunnels to be built and fully operable by 2025.
The tunnel system is a component of a 20-year, long-term plan to reduce raw sewage overflows mandated by the U.S. Environmental Protection Agency and Indiana Department of Environmental Management.
Morgan said Citizens Water has incorporated sustainable concepts into the design of the Deep Rock Tunnel Connector, including the elimination of one of two previously planned pumping stations, saving ratepayers millions of dollars in upfront capital costs and long-term operating costs; improving energy efficiency of operations for long-term reduced environmental impacts; and limiting disruptions of utilities which results in additional savings.
Citizens provides water, wastewater, natural gas, steam and chilled water service to more than 300,000 households and businesses in the Indianapolis area. Citizens is a not-for-profit public charitable trust that has served Indianapolis for nearly 125 years. Last year, Citizens acquired the water and wastewater of utilities of the city of Indianapolis in a $1.9 billion transaction. As part of the transition, most employees of the city utility department and contract operators of water and sewer services became employees of Citizens Water.
FOR MORE INFO:
(440) 248 3303, www.robbinstbm.com
by Jeff Griffin Senior Editor