Title page for ETD etd-09222011-092706


Type of Document Dissertation
Author Adams, Tiffany E
URN etd-09222011-092706
Title Stability of Levees and Floodwalls Supported by Deep-Mixed Shear Walls: Five Case Studies in the New Orleans Area
Degree PhD
Department Civil Engineering
Advisory Committee
Advisor Name Title
Filz, George M. Committee Chair
Brandon, Thomas L. Committee Member
Foti, Roseanne J. Committee Member
Hochella, Michael F. Jr. Committee Member
Mitchell, James K. Committee Member
Keywords
  • Levee stability
  • Deep-mixed shear walls
  • Column-supported embankment
  • Numerical finite difference analysis
  • Failure mode analysis
Date of Defense 2011-09-08
Availability unrestricted
Abstract
Increasing interest, from the U.S. Army Corps of Engineers (USACE) and other agencies, in using deep-mixing methods (DMM) to improve the stability of levees constructed on soft ground is driven by the need to reduce levee footprints and environmental impacts and to allow for more rapid construction. Suitable methods for analysis and design of these systems are needed to ensure that the DMM technology is properly applied.

DMM shear walls oriented perpendicular to the levee alignment are an effective arrangement for supporting unbalanced lateral loads. Shear walls constructed by overlapping individual DMM columns installed with single-axis or multiple axis equipment include vertical joints caused by the reduced width of the wall at the overlap between adjacent columns. These joints can be made weaker by misalignment during construction, which reduces the efficiency of the overlap. Depending on the prevalence and strength of these joints, complex failure mechanisms, such as racking due to slipping along vertical joints between adjacent installations in the shear walls, can occur. Ordinary limit equilibrium analyses only account for a composite shearing failure mode; whereas, numerical stress-strain analyses can account for other failure modes.

Five case studies provided by the USACE were analyzed to evaluate the behavior of levee and floodwall systems founded on soft ground stabilized with DMM shear walls. These identified and illustrated potential failure mechanisms of these types of systems. Two-dimensional numerical stability and settlement analyses were performed for the case studies using the FLAC computer program. The key findings and conclusions for the individual case studies were assessed and integrated into general conclusions about design of deep-mixing support for levees and floodwalls.

One of the significant findings from this research was to identify the potential for a partial depth racking failure, which can control design when the DMM shear walls are socketted into a relatively strong bearing layer. The potential for partial depth racking failure is not discussed in the literature and represents a new failure mode identified by this research. This discovery also highlights the importance of adapting suitable methods for analysis and design of these systems to address all potential failure modes.

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