Washington State sets out costs and delays from SR520 pontoon repairs

The work involves repairing four cracked pontoons from the first construction cycle and modifying another four from the second cycle. WSDOT has agreed to pay the contractors a total of US$71.2m from a risk reserve budget set aside to address unforseen issues on the US$2.7 billion SR 520 programme.

The problems have also put back the opening date, with the new floating bridge now estimated to open to traffic in late 2015 or early 2016. It was originally scheduled to open in July 2015, but could have opened as early as December 2014 under the contractor’s schedule.

In February, WSDOT acknowledged a design error that led to cracks in the initial cycle of concrete pontoons, which also required modifications to the second construction cycle to meet the new bridge’s 75-year design life. At that time, WSDOT estimated repairs would cost tens of millions of dollars.

For the first change order, WSDOT will pay US$48.8 million to the floating bridge contractor Kiewit/General/Manson. This covers the first cycle of crack repairs, which have been under way since June. The repair procedure addresses cracks that developed in the keel slabs and end walls on four of the first six pontoons built in Aberdeen. The repairs feature epoxy injections, transverse post-tensioning and the application of carbon-fibre wrap.

Pontoon W - one of four SR 520 bridge pontoons requiring repairs - framed a view of the Space Needle as it travelled to Harbor Island this month.

For the second change order, WSDOT will pay US$22.4 million to pontoon construction contractor Kiewit-General for the addition of transverse post-tensioning to four pontoons while they were in the casting basin in Aberdeen. The work was completed prior to float-out in April.

Additional change orders to be finalised later this year include adding transverse post-tensioning to the pontoons built in later cycles.

The current bridge, which will be 50 in August, is vulnerable to earthquakes and windstorms and must be replaced. Construction on the replacement began in April 2012 and pontoon construction is under way at two casting basins: one in Aberdeen and one in Tacoma. Eight pontoons recently floated out of the Tacoma casting basin. With the recent Tacoma float-out, 32 of the 77 pontoons needed to replace the bridge are complete.