Physical modelling analysis of the New Orleans levee breaches

As part of the Interagency Performance Evaluation Task Force (IPET) investigation into levee breaches in New Orleans following Hurricane Katrina, centrifuge modelling was undertaken of representative levee cross-sections on the 17th Street, Orleans and London Avenue Canals. Two mechanisms were observed leading to breaching of the levee in the models, both of which stemmed from a water-filled crack that formed in front of the flood wall. Depending on the foundation conditions and geometry of the levee and flood wall, the crack led either to a rotation of the flood wall landwards, with uplift and sliding on the top of the sand towards the landward toe of the levee, or to a translational (sliding) failure in the clay layer commencing from the bottom or toe of the flood wall. In the Orleans models no breach ensued, although it was clear these sections were close to failure. The centrifuge model tests identified, at an early stage in the IPET investigation, the importance of the ‘gap' mechanism affecting the stability of the flood walls, and confirmed that levee geometry and flood wall depth of penetration, together with the underlying soil profile, were critical to the performance of the system under flood loading.