Dissertation/Thesis Abstract

Developing a Retrofitting System to Mitigate Floodwall Failures of New Orleans
by Kidd, James Tyler, M.S., The University of Mississippi, 2011, 129; 1496337
Abstract (Summary)

Hurricane Katrina exposed many areas of weakness in the hurricane protection system in the New Orleans, LA area. In addition, severe damage and catastrophic failures occurred throughout the hurricane protection system. This study focuses on two key aspects of failure: erosion by plunging water and strength reduction of the floodwall due to piping.

Erosion by plunging water was the first failure mode considered in this study. The aim of this research was to mitigate erosion by reinforcing the soil, and also to study the effects the plunging water thickness had on erosion.

The prevention or reduction of erosion using a retrofitting technique or a ground modifier was used for erosion mitigation. The two main ground modifiers that were tested are the Vetiver plant and Polyhedral Oligomeric Silsesquioxanes (POSS). Both modifiers showed improvements in erosion resistance and reduced the total erosion of the samples. The Vetiver plant showed a greater resistance to erosion as compared to POSS. However, the Vetiver plant has limited applicability and also takes a number of years to grow to its full potential. Furthermore, POSS showed less erosion resistance, but is easily applicable to most any soil condition because it is sprayed onto the soil.

To accurately predict the erosion behavior for a real world scenario or a catastrophic event, erosion tests had to be scaled up. One of the most significant factors when dealing with erosion is the thickness of the nap from the plunging water. Consequently, when the thickness of plunging water increases, the amount of erosion should also increase; the rate of this increase is the one of under researched areas. To evaluate this behavior of erosion, tests were conducted with the thickness of plunging water equal to: .0003, .0065, .013, and .2 m. The velocity of the plunging water was kept at a constant 6 m/sec; because this is the expected velocity of plunging water during Hurricane Katrina. Tests were conducted for three different soil samples at the University of Mississippi Erosion Test Bed (UMETB) and also at the USDA-HERU facility in Stillwater, OK. From these tests, it was concluded that increasing the water thickness also increases the equilibrium erosion depth. However, this increase does not follow a linear pattern.

The second failure mode considered in this study was the loss of strength in the underlying levee material due to piping and also the infiltration of water between the soil and floodwall. This infiltration of water between the soil and floodwall was caused by the development of a gap between the soil and floodwall which is a result from the floodwall leaning. When high water pressure (caused by rising water) is exerted onto the floodwall; the floodwall is deformed or leans outward away from the pressure.

This study aimed at preventing the gap formation by inlaying an expansive bentonite and sand mixture. Bentonite is highly expansive, but has a low permeability; therefore, sand is added to increase the permeability which increases the rate of expansion. The mixture was designed to swell and seal the gap formation. After testing several mixtures it was confirmed that bentonite and sand would adequately swell to seal the gap. The mixture that proved most effective was 30% bentonite and 70% sand by weight. It was concluded this mixture was the most effective because: it swelled fast enough to seal the gap with only letting a negligible amount of water infiltration, and also this mixture excerpted low lateral swelling pressure onto the floodwall.

The results of these three topics were documented in the form of three journal papers. This thesis, therefore, presents these results in the draft form of journal papers.

Indexing (document details)
Advisor: Song, Chung R.
Commitee: Al-Ostaz, Ahmed, Cheng, Alex, Hanson, Greg
School: The University of Mississippi
Department: Civil Engineering
School Location: United States -- Mississippi
Source: MAI 50/01M, Masters Abstracts International
Subjects: Civil engineering
Keywords: Louisiana
Publication Number: 1496337
ISBN: 978-1-124-74691-3
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