Multnomah County’s Earthquake Ready Burnside Bridge Project now has a clearer picture of how soil composition will interact with new Burnside Bridge foundations. This comes after several months of work building a 10-foot diameter test shaft (foundation) just north of the Burnside Bridge in Tom McCall Waterfront Park. Construction and subsequent testing finished in March and fencing around the construction site came down Friday, May 2. Check out the project’s time-lapse video for a full look at the test shaft work.
Findings
This work was an important step before construction, to help engineers understand and verify how designs for the new Burnside Bridge foundations will interact with the soil. After crews built the 10 foot test shaft (foundation) which went down 125 feet, they used special equipment that generates extreme pressures to test how the shaft (foundation) would interact with the soil in the event of a major earthquake. Tests found the soil’s load capacity was stronger than originally anticipated. This helped engineers determine the future bridge shafts in Tom McCall Waterfront Park would need to be built down 125 feet. Through these tests, engineers were also able to determine 10 foot shafts are the appropriate diameter for the new Burnside Bridge foundations.
“This was an incredible opportunity for our project,” Multnomah County Test Shaft Project Manager Ryan Rucker said. “With many unknowns surrounding how the soil would interact with the new bridge structures, being able to test its capabilities was invaluable. Thanks to the dedication and expertise of our design consultant and general contractor, we now have a much clearer understanding of the soil strengths. This has enabled our team to refine our design – potentially reducing the number and depth of shafts in various locations – which could lead to cost savings, reduced construction timelines and environmental impacts while building in the river.”
Once the work was complete, crews took down construction equipment and reseeded to allow the site to return to its original state.
Background
This work is part of Multnomah County’s Earthquake Ready Burnside Bridge Project which is now in the Design Phase. Multnomah County is leading an effort to replace the Burnside Bridge with a crossing that’s immediately usable after a Cascadia Subduction Zone earthquake. For project information, visit: https://burnsidebridge.org/.
Multnomah County maintains five Willamette River bridges: the Sellwood, Hawthorne, Morrison, Burnside and Broadway Bridges as well as the Wapato Bridge over the Multnomah Channel. For information, visit: https://www.multco.us/bridges.