Evaluation and Prediction of 17th Street Canal I-Wall Stability Using Numerical Limit Analyses

Numerical limit analyses have been used to evaluate the stability of the 17th Street Canal I-wall levee during Hurricane Katrina. The potential formation of a water-filled gap along the canal-side soil-wall interface at failure is included in both the lower- and upper-bound formulations. The analyses replicate published two-dimensional (2D) cross sections and soil properties developed in forensic investigations carried out by the Interagency Performance Evaluation Task Force (IPET) and by the Independent Levee Investigation Team (ILIT). The current results provide an independent basis for understanding and evaluating the proposed failure mechanisms and demonstrate that a water-filled gap is a necessary condition for the critical I-wall failure mechanism. Further limit-analysis calculations produce credible estimates of the surge elevation that caused failure of the 17th Street Canal I-wall as well as predictions of a consistent failure mechanism. The numerical limit analyses show clearly how differences in the stability of the I-wall are linked to different interpretations of the stratigraphy and undrained shear strengths by IPET and ILIT. The analyses also show that effects of a thin layer of weak organic clay as postulated by ILIT are not necessary to explain the I-wall failure.