An Investigation of the Seismic Response of Earthen Levees with Cutoff Walls with a Focus on the Development of a High Performance Cutoff Wall Material.

In recent years, flood protection systems across the nation have undergone extensive investigation into their current state and adequacy regarding various potential hazards. These investigations have revealed that 1) many existing levees are vulnerable to excessive under- and through-seepage due to the insufficient state or length of their cutoff walls, and 2) seismic activity poses serious risks to many existing levees. Traditional cutoff walls (e.g. slurry-type walls and steel sheet pile walls) have a variety of shortcomings, particularly for levees in seismic regions. This project investigates the feasibility of using a new cutoff wall material that overcomes many of the shortcomings associated with traditional cutoff wall materials. The proposed cutoff wall material is from a family of high performance fiber-reinforced cementitious materials called Engineered Cementitious Composites (ECC). ECC possesses several characteristics that make it ideal for use as a cutoff wall material in seismic regions, including high tensile ductility and small crack width, among others. The initial portion of this study focuses on characterizing the dynamic response of levees with conventional cutoff walls. Two sets of parametric analyses are conducted to investigate how the presence of a cutoff wall affects the dynamic response of a levee and what type of demands are placed on the cutoff wall during the seismic event. One set of analyses is conducted for levees founded on non-liquefiable soils and the other is for levees founded on liquefiable soils. In collaboration with materials science researchers, an ECC material is then tailored for use in the construction of levee cutoff walls. The results of materials testing on the resulting candidate mix design are then used as input in further numerical modeling, in which the dynamic response of levees with ECC cutoff walls is investigated. These analyses are used to assess the feasibility of the candidate mix design. Conclusions regarding the feasibility of using such a material for levee cutoff walls are presented, with recommendations for a candidate ECC mix. Also, revisions to existing levee seismic design guidelines are proposed, based on the results of the parametric analyses of the dynamic response of levees with conventional cutoff wallsPHDCivil EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/110458/1/ajimlobb_1.pd

Factor of Safety Reduction Factors for Accounting for Progressive Failure for Earthen Levees with Underlying Thin Layers of Sensitive Soils

The effects of progressive failure on flood embankments with underlying thin layers of soft, sensitive soils are investigated. Finite element analysis allows for investigation of strain-softening effects and progressive failure in soft and sensitive soils. However, limit equilibrium methods for slope stability analysis, widely used in industry, cannot capture these effects and may result in unconservative factors of safety. A parametric analysis was conducted to investigate the effect of thin layers of soft sensitive soils on the stability of flood embankments. A flood embankment was modeled using both the limit equilibrium method and the finite element method. The foundation profile was altered to determine the extent to which varying soft and sensitive soils affected the stability of the embankment, with respect to progressive failure. The results from the two methods were compared to determine reduction factors that can be applied towards factors of safety computed using limit equilibrium methods, in order to capture progressive failure