Abstract:
Portland, Oregon is one of Americas great bridge cities. The Burnside Bridge is one of eleven signature structures that exist over a 16-mile stretch of the Willamette River. Located on one of the busiest streets in Portland, it is designated as an official emergency transportation route in case of earthquake or disaster. Gustav Lindenthal’s 1926 Burnside Bridge is a historically significant structure listed in the National Register of Historic Places. Although it has been seismically retrofitted multiple times in the last several decades it is no longer considered seismically resilient, therefore a new earthquake ready Burnside Bridge is underway.
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The new foundation design will make use of large diameter drilled shafts, super piles if you will, that are so well inclined to satisfy the major design criteria driven by high axial loads, liquefaction-induced settlement, and lateral spreading. Load resistance for the new drilled shafts will be met by extending them through liquifiable fine-grained alluvium, gravel alluvium, and deep into the lower Troutdale Formation. A far cry from Lindenthal’s 1926 river piers supported on a veritable pin cushion of 40-foot-tall Douglas fir tree trunks tipped into Gravel Alluvium.
Multnomah County (Owner) is using the Construction Manager General Contractor (CM/GC) delivery method for this project to get early contractor input and collaboration with designers. Everyone involved emphatically recognized the benefits of a pre-construction drilled shaft load test program to obtain essential information for the drilled shaft geotechnical design and constructability.
And so, the team embarked upon installation and testing a full-sized dedicated test shaft with a diameter of 10 feet and a length of 130-feet. Load testing such a super pile required double levels of bi-directional cell assemblies with an astounding 51,000 tons of total jacking force. With successful completion of this ultra-high load test, it defeats the previous world record set in Dubai bringing the world record back to US soil.
This is a story of a monster load test on a super pile.