Paula Wallis TunnelTalk

Fig 1. East Side CSO alignment

Ahead of schedule and under budget, Portland is closing in on a major milestone on its Willamette River East Side CSO tunnel project. Kiewit-Bilfinger Berger (KBB) JV is nearing the end of the first 21,000ft (6.4km) drive with less than 1,700ft left to go before breakthrough into the Port Center Shaft (Fig 1).

Paul Gribbon, Willamette CSO Tunnel Chief Engineer for the City of Portland Bureau of Environmental Services, reported on Wednesday (September 9) that the 7.7m diameter Herrenknecht Mixshield has completed more than 90% of the north drive and is anticipated to breakthrough into the Port Center Shaft by the end of October, 2009.

"The porject has been going extremely well," said Gribbon. "Kiewit-Bilfinger Berger JV is still ahead of their baseline schedule and we're tracking about $30 million+ under our expected expenditures at this point."

Gribbon attributes the so-far successful project to the structure of the contract that spreads the risk between the owner, designer and contractor.

"The contractor was selected through a qualifications-based selection process at about the halfway point of the design phase and was under contract prior to design completion. The construction contract is a cost-reimbursable/fixed-fee contract. This has resulted in a three-way partnership among the owner (City of Portland), designer (Parsons Brinckerhoff) and contractor (Kiewit-Bilfinger Berger JV) throughout the construction period which has resulted in a rapid response to construction challenges, quick on-site decisions, a number of cost savings, and no disputes."

TBM trailing gear

Gribbon said that a similar three-way partnership between designer Parsons Brinckerhoff, contractor Impregilo/SA Healy JV, and the owner, also worked well on the earlier $269 million West Side CSO project. Excavation of the 3.5-mile, 14.5ft diameter soft-ground tunnel, along the west bank of the Willamette River was completed in July, 2005 with the tunnel fully operational in September 2006.

KBB was awarded the $381 million East Side tunnel contract - touted as the largest public works contract in Portland's history - in February 2006. The city budgeted $464 million for the project including $38 million set aside for contingencies and $45 million for excalation.

Inside Opera Shaft

Prior to the construction contract KBB was awarded the $1.5 million preconstruction services contract that included design review and assistance,the estimated reimbursable cost and schedule, a jointly developed risk analysis, and development of project-specific programs such as safety, quality and subcontracting plans.

The TBM started boring in May 2007 from the Opera Shaft and is moving north towards the Port Center Shaft at the Swan Island Pump Station. During the 28 months of excavation the TBM has achieved a best day of 115ft and a best week of 421ft, which happened to be a six-day week. The contractor typically runs three shifts over a five-day week.

The seven shafts along the entire East Side alignment are about 49ft - 60ft in diameter and 110ft to 165ft deep.

Once the TBM arrives at the Port Center Shaft, it will be removed, placed on a barge, and brought back upriver to the Opera Shaft. "It will then be relaunched for the remaining 8,800ft drive south to the McLoughlin Shaft," said Gribbon. "Most of the connecting pipeline work has been completed but work is continuing on the buildout of the main shafts."

When the entire 20-year, $1.4 billion CSO control program is completed in 2011, it will reduce CSO volume into the Willamette River by more than 94%.

References

Portland progress - TunnelTalk, Aug 2008