In addition to being the capital of the Hoosier state, Indianapolis, Indiana, is famous for being the home of the Indianapolis Motor Speedway, the storied famous 2.5-mile track that is home to some of the world’s most celebrated open-wheel and stock car races. But as fans flock to the fabled raceway, they have little knowledge of the powerful machine racing underground in an effort to provide clean waterways in and around the city.
The DigIndy Tunnel System is a 28-mile long network of 18-ft ID deep rock tunnels being built 250 ft beneath the city. The $2 billion program, which includes tunnels and plant upgrades, will reduce combined sewer overflows (CSOs) by up to 99 percent, keeping Citizens Energy Group and the City of Indianapolis in compliance with a consent decree.
To put the scale of the DigIndy program in perspective, it would take a race car less than 20 trips through the large-diameter sewer network to complete 500 miles, compared to 200 circuits around the speedway.
Fittingly for Indianapolis, the TBM being used for the project – that’s right, one TBM for the entire 28-mile network – set excavation records along the way. As the project is speeding to the finish line and portions of the network have been activated, TBM: Tunnel Business Magazine in partnership with the Breakthroughs in Tunneling Short Course has recognized the DigIndy program as the winner of its 2021 Tunnel Achievement Award for Project Excellence.
Established in 2012, the Tunnel Achievement Award recognizes projects that are successfully completed and demonstrate innovation and teamwork, and provide benefits to the community. The award is presented annually at the Breakthroughs in Tunneling Short Course, which is scheduled for Sept. 13-15, 2021, on the campus of the University of Denver in Colorado.
While overall tunnel excavation is not yet complete, five of the six tunnel segments have been excavated with the sixth and final segment approximately 20 percent complete.
The DigIndy Tunnel System was conceived as a result of a consent decree between the City of Indianapolis, the U.S. EPA and the Indiana Department of Environmental Management to reduce CSOs in the Indianapolis area. In 2011, Citizens Energy Group, a public charitable trust, purchased the water and wastewater assets from the City, thus becoming a party to the consent decree and inheriting ownership of the tunnel program.
The final configuration of the DigIndy program consists of six interconnected tunnel projects. Each of the tunnels are mined with the same 20-ft, 2-in. OD Robbins Main Beam TBM and lined with 1-ft thick concrete walls. All of the tunnels were completed by the same contractor, a joint venture of J.F. Shea and Kiewit.
The tunnel segments are:
- Deep Rock Tunnel Connector: 39,362 lf of tunnel; 3 CSO connecting structures/deaeration chambers and adits.
- Eagle Creek Tunnel: 9,175 lf of tunnel (added as a change order to the Deep Rock Tunnel Connector project); one CSO connecting structure/plunge drop.
- White River Tunnel: 30,628 lf of tunnel; 2 bifurcations; 7 CSO connecting structures/deaeration chambers and adits.
- Lower Pogues Run Tunnel: 10,182 ft, bifurcates from White River Tunnel; 2 CSO connecting structures/deaeration chambers and adits.
- Fall Creek Tunnel: 20,244 lf of tunnel; 10 CSO connecting structures/deaeration chambers and adits.
Pleasant Run Tunnel: 41,472 lf of tunnel; eight CSO connecting structures/deaeration chambers and adits.
At the time Citizens acquired the water and wastewater assets in August 2011, the first portion of the DigIndy Tunnel System – the Deep Rock Tunnel Connector – had been designed and was in the process of bidding. Citizens inherited the project and awarded a low-bid contract to the joint venture team of Shea-Kiewit (SK) in December 2011.
The Deep Rock Tunnel Connector broke ground in 2012, and in early 2013, a refurbished Robbins Main Beam TBM, originally built in 1980, began excavating the limestone and dolomite rock from the Southport Treatment Plant. Crews experienced early success with the combination of TBM, belt conveyor system and favorable rock conditions by setting speed records for TBMs in the 6- to 7-m range, 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).
As the Deep Rock Tunnel Connector progressed, Citizens and SK negotiated a change order to reconfigure the Eagle Creek Tunnel, initially envisioned as a soft ground interceptor, as a deep, large-diameter tunnel, providing an additional 17 million gallons of storage. To build the tunnel, SK backed up the TBM 11,000 ft from the end of the Deep Rock Tunnel Connector and bifurcated a spur to mine the redesigned Eagle Creek Tunnel – a process that would be repeated later in the program.
“By my calculations, we will have backed up the TBM a total of about 9 miles, which is more than some cities go forward,” said Mike Miller, Manager of Citizens Energy Group’s DigIndy Capital Program. “The ability to back up the machine has been a unique aspect of the DigIndy Tunnel System. It has allowed us to reduce a number of large diameter shafts and save cost.”
The Deep Rock Tunnel Connector and the Eagle Creek Tunnel have been fully excavated and lined, and put into service in 2017 ahead of the milestone date, allowing Citizens to begin to realize water quality benefits as the follow-on tunneling segments continued into construction.
As the Deep Rock Tunnel Connector/Eagle Creek Tunnel moved toward an early completion, project planners began looking ahead to the next phases of work. With a number of other cities preparing to put projects out to bid at the time, and with a potential labor shortage looming, Citizens accelerated solicitation for its White River Tunnel and Lower Pogues Run Tunnel segments, which were combined in a single package.
Citizens invited contracting firms to submit on White River/Lower Pogues Run, with the option of having solicitors include an alternate proposal to include the Fall Creek Tunnel and Pleasant Run Tunnel segments. Citizens accepted a proposal from Shea-Kiewit to construct all four tunnel segments based on best value, which factored in price, approach, teaming structure, schedule and participation of minority-owned, women-owned and veteran-owned businesses. The fact that White River and Lower Pogues Run solicitation was completed a year earlier than originally planned, allowed Shea-Kiewit to propose its scheme of using a single TBM to mine all 19 miles of the remaining tunnels and meet the EPA-mandated service deadline of Dec. 31, 2025. The contract for the remaining tunnels was executed in June 2016.
After refurbishment, the TBM was launched from the 35-ft diameter shaft previously built as the retrieval shaft for the Deep Rock Tunnel Connector to begin the next phase of tunneling. Mining of the White River Tunnel alignment extended approximately 4,800 ft, at which point mining followed the Lower Pogues Run Tunnel alignment. Following completion of the Lower Pogues Run Tunnel, SK backed the TBM down to a bifurcation, and continued with the remainder of the White River Tunnel.
Both the White River Tunnel and Lower Pogues Run Tunnel are expected to go online this year.
Mining on the Fall Creek Tunnel commenced in September 2019 from a 30-ft diameter shaft that was previously constructed as the retrieval shaft for the White River Tunnel alignment. After successfully mining the White River Tunnel, the TBM mined through the shaft and underwent a minor refurbishment. Mining was completed on April 1, 2020.
The tunnel terminated approximately 2,400 ft past the retrieval shaft location. The TBM was backed up and parked downstream of the shaft, and the remainder of the shaft was shot down to the invert. The TBM was retrieved and transported to the site of the Pleasant Run Tunnel launch shaft, where it underwent a full refurbishment before beginning the Pleasant Run Tunnel – the final leg of the DigIndy system.
As of mid-July, SK was tracking ahead of schedule and had mined 9,000 ft of the 41,000-plus ft Pleasant Run Tunnel. SK will mine to an intermediate shaft about halfway through the alignment and transfer muck removal operations to that shaft.
SK is working on lining completed tunnel segments using seven 35-ft Everest forms. According to Miller, SK is able to line an average of 245 ft of tunnel per day. In one short section of tunnel where ground was more challenging and groundwater was present, SK used a PVC membrane from Renesco between the liner and tunnel wall to ensure that extraneous water does not enter the system.
In addition to the tunnel works, plant updates, drop shafts, surface works and consolidation sewers are part of the program and are active across the city, with nearly 30 active construction sites as of July. Local contractors F.A. Wilhelm and Bowen Engineering have both played large roles in surface and near surface works.
Keys to Success
While mostly good ground conditions have played a role in the success of the project to date, Miller stresses that open communication is another key factor. “We have had a good relationship with the contractor that has helped the program,” Miller said. “It has allowed us to get their input on design and constructability issues. By establishing a strong relationship, we are able to negotiate in good faith.”
Miller points out two particular areas where this has proven beneficial for the program: flexibility and risk sharing.
When the contract was awarded in 2016 for the White River, Lower Pogues Run, Fall Creek and Pleasant Run tunnels, designs were not fully developed, particularly for Fall Creek and Pleasant Run which were farther out from construction. This meant that SK was contracted to perform work that had yet to be defined, yet both parties were able to work together to make adjustments as the work and the designs progressed. (The contract did contain an out clause for the Pleasant Run Tunnel in case the parties were unable to reach an agreement.)
As for risk sharing, Miller says that Citizens opted not to use a dispute review board (DRB) based on their experience on Deep Rock Tunnel Connector and complex change orders Citizens and SK were able to successfully navigate. The parties were also able to come up with risk sharing ideas that helped to reduce cost while fairly compensating the contractor if extra work is required.
As an example, the geology within the bedrock is mostly dry, but the presence of water can require crews to cut off water flows with grout. In this case, Citizens and SK agreed on a plan where SK would be compensated on an agreed-upon hourly rate when crews were forced to stop tunneling to initiate grouting.
“The biggest thing is open communication, just sitting down and talking about the project: What is coming up? What are the potential pitfalls?” Miller said. “Having a personal relationship helps work through difficult times.”
About the TBM
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, as well as projects in Massachusetts and Canada. 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.
Owner: Citizens Energy Group
Designers: AECOM (Deep Rock Tunnel Connector, Eagle Creek Tunnel); Black & Veatch (Lower Pogues Run Tunnel, White River Tunnel, Fall Creek Tunnel, Pleasant Run Tunnel)
Construction Managers: AECOM
Owner’s Third-Party Consultants: Brierley Associates
Suppliers: Robbins (TBM)
Combined Consolidation Sewer Contractors: F.A. Wilhelm, Bowen Engineering Corp.
Lifetime Achievement Award for Exceptional Service and Contribution to the Tunneling and Underground Construction Industry: Gary Brierley
The Breakthroughs in Tunneling Short Course is pleased to announce that Dr. Gary Brierley, P.E., is the recipient of the Lifetime Achievement Award for Exceptional Service and Contribution to the Tunneling and Underground Construction Industry.
“ I have known and worked with Gary over the last four decades and have always been impressed with his vast knowledge and his practical approach to all aspects of tunnel design and construction,” said Levent Ozdemir, director of the Breakthroughs in Tunneling Short Course. “His contributions to the advancement of the tunneling industry are endless. Gary has also been a passionate educator and mentor to students and young professionals involved in tunneling. He frequently served as a guest lecturer in my tunneling classes at the Colorado School of Mines and the students always enjoyed his lectures.”
Brierly, President of Dr. Mole Inc., has more than 50 years of experience with both the technical and nontechnical aspects of underground engineering and construction management. Beginning as a project manager in 1970, he has worked on more than 1,000 projects involving all types of underground design and construction including soil and rock engineering, building foundations, braced excavations, ground improvement and slope stability for owners, contractors, engineers, public agencies, and attorneys
Brierley earned a bachelor’s degree in Civil Engineering from Tufts University and masters and doctoral degrees from the University of Illinois in 1970 and 1975, respectively. During that time Brierley was fortunate to work on the instrumentation program for DuPont Circle Subway Station in Washington, D.C., a project that formed the basis for his doctoral dissertation.
Since that time, Dr. Brierley has devoted his entire professional career to the design and construction management of underground openings. Dr. Brierley has been involved with two successful start-up firms providing consultation services for underground projects: Brierley and Lyman and Brierley Associates. He has served as President of the American Underground Construction Association, Chairman of the Underground Technology Research Council, and as a member of the U.S. National Committee on Tunneling Technology. He has been a member of several professional societies and has authored more than 200 technical papers and articles for tunneling publications including the “Ask Dr. Mole” column for TBM magazine.