Modeling of Downdrag Bending Moments in Floodwall Support Piles
The presence of fill material produces downdrag bending moments in batter piles that support T-Wall structures in the Greater New Orleans Hurricane and Storm Damage Risk Reduction System. These loads may induce premature flexural failure and prohibit the system from retaining the designed level of storm floodwater. The United States Army Corps of Engineers, as a result of the devastation caused by Hurricane Katrina in New Orleans, has launched an initiative termed Actions for Change. It strives to dramatically improve the understanding and condition of the entire infrastructure owned or operated by the USACE. This creates the need for extensive research on soil and soil-structure systems to improve both existing and future structures such that there are no failures of those systems.
Rensselaer Polytechnic Institute and the United States Army Corps of Engineers have collaborated on several high-profile projects. RPI was directly involved with the USACE in the evaluation and analysis of the flood protection system in New Orleans after Hurricane Katrina. Furthermore, the influence of unstable soil movement on T-Walls was recently tested at the RPI facility. Therefore, the institute is intimately aware of the needs related to modeling of that infrastructure.
In general, the T-wall systems in New Orleans performed very well during previous hurricanes and high water loading. However, recent observations show that fill material is inducing bending moments in their support piles via loading of the foundation soil. Calculations indicate that these bending moments may be near the ultimate capacity for typical piles. The US Army Corps of Engineers has contracted Virginia Tech to produce numerical models of the physical phenomena. Physical modeling and numerical simulations are complimentary, often resulting in a stronger and more robust understanding. There is a substantial benefit in performing centrifuge modeling, which offers all the benefits of full-scale physical modeling but at a lower cost and faster time to completion. The project will comprise the physical modeling of typical T-Wall sections, whose geometry is provided by USACE, in order to obtain the batter pile bending moments in response to different loading stages. The models will be instrumented with various sensing technologies, including strain gages on the support piles, pore-water pressure sensors in the foundation soil, displacement tracking targets in the soil, and cantilever resultant detectors on the foundation elements. Cameras will be mounted at several locations and these will record the progress of the testing. The recorded videos will be processed using motion-tracking software to produce soil displacements. Therefore, the following information will be obtained: axial forces in the support piles, bending moments in the support piles, true and excess pore-water pressure in the foundation soil, soil displacement and deformations, and wall rotation (in the case of asymmetric loading). Combined with the numerical models, the results will provide valuable insight into the behavior of the system.