The U.S. Army Corps of Engineers Hurricane Katrina Interagency Performance Evaluation Task Force (IPET) has released video footage of a small-scale centrifuge model of the 17th Street Canal. Made by researchers at Rensselaer Polytechnic Institute, the video illustrates the preliminary findings from the March 10, 2006 IPET status report to the American Society of Civil Engineers (ASCE) review committee, which indicated that the 17th Street levee may have slid on a layer of weak clay just beneath the peat that underlies the earthen structure.
As part of the ongoing IPET study, Rensselaer engineers were selected to build and test small-scale centrifuge models of sections of the flood-protection system from several locations in New Orleans, including the 17th Street Canal and the London Avenue Canal. They are attempting to replicate conditions during Hurricane Katrina by subjecting the models to flood loads.
Tarek Abdoun, associate professor of civil and environmental engineering at Rensselaer, will be presenting the team’s preliminary findings March 20 in New Orleans at a public meeting of the National Academies review committee. “Our centrifuge models have already produced some valuable information, which not only will provide the Corps with important scientific data as they move forward, but also could give engineers around the world a better understanding of how levees respond under extreme conditions,” Abdoun says.
To date, three small-scale models have been tested at Rensselaer and at the Corps’ Engineer Research and Development Center (ERDC) in Vicksburg, Miss. Models of the London Avenue Canal and the 17th Street Canal were run at Rensselaer. In the 17th Street model, the wall in the middle of the earthen structure started to move before the water reached the top, according to Abdoun. He also notes that the weak clay directly underneath the peat layer sheared first, causing the whole levee to slide.
Abdoun stresses that these results are still preliminary, and they need to be replicated at both Rensselaer and ERDC. He and his colleagues are currently examining data from the initial trials, in preparation for an additional series of tests that will be carried out in the coming weeks.
“Until all the physical evidence has been analyzed, we will not have a complete picture of what happened,” says Thomas Zimmie, professor and acting chair of civil and environmental engineering at Rensselaer. Zimmie also was a member of the National Science Foundation-funded team that investigated levee failures in the immediate wake of the storm.
The project takes advantage of the facilities at Rensselaer’s Geotechnical Centrifuge Research Center, which is partially funded through the National Science Foundation (NSF). Rensselaer’s 150 g-ton centrifuge — one of only four of its kind in the country — has a large mechanical arm that can swing model structures around at 250 miles per hour, exerting forces real structures would face only at catastrophic moments.
The IPET final report, which is scheduled to be completed by June 1, will be validated by an external review panel from the American Society of Civil Engineers (ASCE). The National Academies has assembled a multidisciplinary, independent panel of acknowledged experts to review and synthesize the IPET and ASCE efforts. The National Academies panel will report its findings and recommendations directly to the Assistant Secretary of the Army for Civil Works in the summer of 2006.
Other staff at Rensselaer’s Geotechnical Centrifuge Research Center working on the project including Inthuorn Sasanakul, facility manager; Javier Ubilla, geotechnical lab engineer; Hassan Radwan, system programmer; Dominic Moffitt, electrical lab engineer; and Alex Sankovich, mechanical lab engineer. The center is part of NSF’s nationwide Network for Earthquake Engineering Simulation (NEES).
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