| Effective design and construction of levees is vital in protecting civilians and infrastructure that are situated in flood-prone regions around the world. In the United States, the city of New Orleans and the state of Louisiana are reinforcing their current levees, known as the Hurricane and Storm Damage Risk Reduction System. The United States Army Corps of Engineers and Rensselaer Polytechnic Institute formed a partnership following Hurricane Katrina in order to investigate the mechanisms behind I-Wall failures. Consequently, I-Walls were deemed unsuitable for retaining floodwater heights greater than 1.2 meters. Pile-founded concrete floodwalls, commonly known as T-Walls, are an effective replacement alternative. They are supported by piles, battered and vertical, and contain a sheet pile cutoff wall for seepage and gradient purposes. Weak foundation soils pose a challenge in their design due to the potential instability generated by storm surge. Previous design methodologies assumed that the unbalanced forces generated in the soil would be resisted by the sheet pile and then transferred to the support piles via the concrete mat. However, recent numerical models indicate that the sheet pile will provide little to no resistance and that the support piles actually ensure stability.;In order to study the effect of the sheet pile with respect to global instability, a series of centrifuge tests were designed to isolate and identify key parameters. The models simulated a generalized floodwall and matched strategic prototype properties using a 1:50 scale. The foundation soil was characterized through in-situ full-flow penetrometer testing and compared with several standard laboratory tests. The behavior of the clay itself was established via a base case test, which did not include support piles or a sheet pile cutoff. Furthermore, the fixation of the piles was tested in order to corroborate the correct failure mode of the system. Finally, the effects of pile spacing and the presence of the sheet pile wall were identified by varying each parameter over several tests. The data from these experiments indicates that the support piles, and not the sheet pile, predominantly resist the unbalanced forces. Data from the centrifuge tests was used to calibrate a numerical model and lead to a new USACE design methodology. |
