Salini Impregilo is awarded US$153.4 million construction of the 4.5km Dugway Storage Tunnel as part of the second phase of tunnelling on Northeast Ohio Sewer District’s US$3 billion 25-year CSO program: Project Clean Lake.
|Table 1. Dugway Tunnel bid spreads|
|Contractor||Bid value US($)|
The Italian company’s bid came in barely £2m dollars under that of nearest rival Southland, but significantly less than the Engineer’s Estimate of $179 million.
Project scope includes TBM excavation of 4,500m x 7.3m i.d. of CSO storage tunnel at a depth of up to 61m. It also includes construction of six shafts of varying diameters and depths, connections between the tunnel and the shafts, and a series of concrete structures for the collection and transportion of wastewater and rainwater. A construction period of 50 months is scheduled.
At the tunnel’s northernmost point it will connect with the $197 million 5.5km-long Euclid Creek Storage Tunnel (ECT) (Fig 1). Excavation of the ECT was completed at the end of a 14 month-drive through a predominant Chagrin Shale geology, on August 21 last year (2013) by the McNally/Kiewit ECT joint venture. An 8.2m diameter open faced Herrenknecht rock TBM was used to complete that drive, part of which runs under Lake Erie itself. A one pass segmental lining system – designed by the client’s lead designer Hatch Mott MacDonald (HMM) – was used for the ECT, and will be used again on the Dugway Tunnel.
The use of steel-fiber-reinforced concrete segments as part of the one pass lining during construction of the ECT cut four months from the construction schedule and saved the sewer district considerable costs. The sewer district plans to use similar techniques for its Dugway tunnel, for which HMM is this time considering the use of plastic fiber reinforcement instead of steel.
The Dugway Tunnel is the second of seven major tunnels (Fig 2), totalling 33.5km in length and with an estimated underground construction cost of $1.33 billion, that together form part of Northeast Ohio Sewer District’s 25-year Long Term Control Plan. The measures will enable the District to comply with Clean Water Act regulations aimed at cleaning up overflows into lakes and rivers across the USA. Project Clean Lake was granted its Consent Decree in 2010 by the Federal Environmental Protection Agency.
The next scheduled procurement is for the 3km-long x 5.2m i.d Doan Valley Tunnel, construction of which is scheduled to start in 2017. That project is about to go into detailed design, and a request for proposals has been called by the project owner
The other tunnels, and their procurement schedules are:
Once completed the Dugway Tunnel and ECT will together provide 117 million gallons of storage capacity during periods of heavy rainfall, reducing the frequency with which combined wastewater and rainwater has to be diverted into Lake Erie so as not to back up the sewage system.