Few cofferdams remain

From ODOT-

In order to construct the new Willamette River Bridge, crews need to reach the riverbed to build the bridge foundations. It would be impossible to work safely to drill shafts and install the bridges piers fighting the river’s current. But by building cofferdams, temporary steel or wooden enclosures that keep water and soil out of the work area, the crews can safely and quickly complete their work – all with the water whizzing by.



On the WRB, crews built nine cofferdams for column construction. Once the columns are complete, crews remove the cofferdams, letting rock and dirt fill in around the base of the columns.

Workers build a column inside a cofferdam on the Willamette River's north bank.

Now that the foundations are complete and the arches are taking shape, we’re approaching another milestone: by the end of summer, crews will remove all but one the project’s cofferdams.



The cofferdam located in the center of the river at the base of the two arches will remain until the bridge is complete.

This cofferdam protects workers as they install rebar for bridge arches in the center of the river.

Supporting the bridge columns, Part 1

From ODOT-

In addition to two graceful arches supporting the bridge, the new northbound Willamette River Bridge will have nine columns, supported by 22 drilled shafts filled with concrete, which create the foundation for the columns.



The team surveyed and staked column locations before clearing and constructing cofferdams at each site. Next, crews built platforms to accommodate a large drill rig near each cofferdam.



The drill rig can drill to a depth of 200 feet, though for this project, the average depth is 35 feet. The bit or auger attached to the drill rig varies in size, but is typically 8 feet in diameter and 6 feet long. Once the drill is positioned, the drilling takes one to two days per shaft.

The drill rig positioned beside the cofferdam is ready to drill one fo the two shafts at this site.

Initial drilling is usually through soft material, which is removed from the hole. To prevent soil from falling back into the hole, workers insert a temporary steel casing (below) before pouring the shaft.

Building cofferdams is the first step in building the new northbound bridge

From ODOT -
With the temporary bridge removed, construction on the new northbound Willamette River Bridge drilled shafts will begin early in the new year. We plan to open this bridge to traffic by fall 2013. Before then, a lot of work needs to be done.
A critical first step is constructing cofferdams. These temporary enclosures keep water and soil out of the work area while we build new bridge footings and shafts in the river and on each bank.
To build our cofferdams, crews drive sheet piles deep down to the bedrock to establish a enclosure. They then excavate soil from inside the enclosure. Water may be needed to be pumped out to create a dry and safe work space.
When the cofferdams are finished, we will use large drilling equipment to bore holes deep in the ground so workers can install steel reinforcement and pour concrete shafts to provide support for the bridge columns.
We’ll have more photos and details on building the new bridge as construction work continues.
This photo shows one of the cofferdams from the southbound bridge.