The Shea/Kiewit (SK) Joint Venture is in final negotiations with the Citizens Energy Group (CEG) prior to expected award next month of a US$500 million build only contract for TBM excavation of the remaining 28km of tunnels needed to complete the 40km x 6.1m (20ft) o.d. deep-level CSO storage tunnel system for Indianapolis.
As part of a closed tendering procurement, an owner-selected number of contractors were invited to bid the project, but in the event the only competition to SK was from the Renda/Southland JV.
Speaking to TunnelTalk from Indianapolis, CEG Underground Construction Director John Trypus confirmed that the refurbished Robbins TBM that completed the project’s main Deep Rock Tunnel Connector (DRTC) drive in July 2014 is currently undergoing contractor refurbishment ahead of scheduled launch on the next 8,530m (5.3-mile) section (the White River Tunnel) in July.
Three other tunnels – the Lower Pogues Run, the Pleasant Run and the Fall Creek Tunnel - will be constructed as part of the same contract, plus a further five deep-level launch/reception and intermediate shafts.
SK, which was also awarded the DRTC shaft and excavation contract in 2012 for a contract sum of US$180.2 million, is currently half way through the 30cm (12in) cast in place lining of the Deep Rock Tunnel Connector, and only last month completed the cast in place lining of the Eagle Creek spur tunnel. It will begin excavation of the White River Tunnel as an extension of the DTRC at its northern end using the reception shaft of the excavated DTRC as its launch shaft.
The drive will be the third of a six-tunnel system, after project owner CEG contracted SK at short notice in 2015 to complete the additional 2,736m (1.7-mile) deep-level Eagle Creek Tunnels pur tunnel. Engineering consultant AECOM, which also designed the DRTC, was called in to complete the design at short notice and delivered in just 90 days. Originally the tunnel in this location had been planned along a shallower soft-ground alignment, and later in the overall program. Accelerating its construction and running it at deep level through competent limestone worked out as a better solution in terms of cost, schedule and surface disruption, Trypus told TunnelTalk.
“Right now the contractor is refurbishing the TBM outside the White River launch shaft, with onsite assistance from the original manufacturer, Robbins,” said Trypus. The 6.1m (20ft 2in) diameter main beam gripper TBM, which broke a whole series of advance rate records during the DRTC drive, is 36 years old and prior to Indianapolis was used on the Second Avenue Subway in New York City. “The latest refurbishment mainly consists of replacing the bearings and the hydraulic systems,” said Trypus. The machine was completely rebuilt and redesigned by Robbins in 2012, specifically for the predominant limestone and dolomitic geology of the Indianapolis area.
“Originally we were going to start TBM excavation of the White River Tunnel in June 2017, but by accelerating the program a year we can continue using just the one machine, although we did consider using two, and we have made savings on this package of about US$70 million as a result,” said Trypus. In fact the project is currently some US$400 million under its projected 2012 cost of US$2.1 billion; two years ahead of construction schedule; and on target to eliminate 99% of combined sewage overflows into the city’s rivers and creeks rather than the 95% figure that was originally mandated under the terms of its Federal Consent Decree.
|Table 1. Six deep-level tunnels of the DigIndy project|
|Deep Rock Connector*||12,231m||6.1m||3|
|Lower Pogues Run||2,735m||6.1m||3|
Notes: *=TBM excavation completed
Careful planning of the TBM drive strategy has also cut down on the number of deep shafts that are required, and use of bifurcations at two locations has saved the need for reception shafts at the end of both the Pogues Run Tunnel and the already completed Eagle Creek Tunnel.
Trypus explained: “The TBM now has a segmented cutterhead which means that the construction team was able to back up the machine [following breakthrough into the DRTC reception shaft] and then excavate the 1.7 mile (2,736m) Eagle Creek spur tunnel from a bifurcation further back along the Deep Connector alignment.” At the end of that drive, in late 2015, the TBM was again backed up to the bifurcation chamber and transported back up the Deep Connector to the reception shaft for extraction and refurbishment.
This process will be repeated again during construction of the 8,530m White River Tunnel. Approximately a quarter of the way into that drive a bifurcation will be constructed enabling the TBM to deviate eastwards for completion of the 2,735m Pogues Run. The machine will then be backed up to the bifurcation point before continuing north for completion of the White River Tunnel in late 2018/early 2019.
Since the 5,954m Fall Creek Tunnel is a continuation of the White River Tunnel, the machine will not need to be extracted and will drive straight through. The only machine extraction remaining will come at the end of that drive, ahead of 9km surface level transportation to the launch shaft for the final 10,621m drive of the Pleasant Run, which is scheduled to start in 2019 and achieve final breakthrough 18 months later.
For the most past the geology across all the deep-level tunnels – all at 200ft or more below the surface – consists of the hard rock of the limestone and dolomite formations. This has made for rapid excavation rates, although variable groundwater levels have resulted in higher-than-expected water inflows at a number of locations. This has presented contractual challenges, notably during excavation of the Eagle Creek Tunnel.
“It was here that we decided to modify our strategy and eliminate our Dispute Review Board (DRB) approach to Differing Site Conditions (DSC),” explained Trypus. Heavy inflows during excavation of the Deep Rock Connector had already led to a successful DSC claim of US$1.3 million by the contractor as contractual compensation for lost time and extra grouting. When another high water inflow event occurred during excavation of the Eagle Creek spur tunnel the owner decided as part of a new round of DSC negotiations with the contractor to adopt a new approach to risk sharing going forward.
“At this point we made a decision as owner to ask ‘what is a better way to deal with this?’ This led to the question: ‘what if we go to the extra expense of probing ahead of the face?’ and the contractor agreed with this, and that it would eliminate some of their risk also.
“So, as part of the new risk sharing agreement, which will remain in place as part of the contract for the remainder of the deep tunnel excavations, the contractor is now required to probe ahead of the machine to determine the need for pre-excavation grouting. We now have in place a system of set tolerances so when the contractor exceeds inflows of 10 gal/min or more the owner pays, on a unit cost, for grout. This shares the risks and helps deal with the unknowns going forward,” explained Trypus.
In the meantime, design by Black and Veatch of the White River, Lower Pogues Run and Fall Creek tunnels is completed, with 30% of design completed on the last tunnel – the Pleasant Run – for which excavation is due to start in 2018/19. TunnelTalk will continue to report on progress.