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Matoc HPP WBV-60 Westwego Floodwall Interim Phase I

Downtown New Orleans flood after Katrina

On August 29, 2005, Hurricane Katrina destroyed and caused significant damage in southwest Louisiana. Hurricane Rita followed this storm on September 24, 2005 and landed on the Louisiana-Texas state line. Since these storms, the U.S. government has funded projects to raise the level of protection for residences and businesses in the New Orleans area.

Raito performed Deep Soil Mixing (DSM) for the WBV Hurricane Protection Project for the U.S. Army Corps of Engineers, New Orleans District.  This project included reinforcing flood walls for higher water events in the Westwego to Harvey area.


Exposed columns from test section

DSM stabilization was performed along the protected side of the existing flood wall between Lapalco Boulevard and Westwego pump station 2. Elements were laid out in a grid pattern, with DSM shear walls oriented perpendicular to the flood wall on 8-ft. centers and a DSM longitudinal wall running parallel to the flood wall.

In-situ soft silts and clays had variable and often high moisture contents. Variable organic content was high, approximately the first ten ft. from the ground surface. Raito studied the properties of the organic matter before the specified test section was started. The chemical testing results showed that organic matter included approximately 5% Hemic and Fulvic acids and 15% ignition loss. These acids generally block cement materials' cementation and pozzolanic reaction at 1% content. Also, the density of the soil cement deteriorates when ignition loss is 10% or more.


Cores of in-situ DSM

Raito performed physical trenching to remove organic matter at shallow depths and used a unique injection system for the first ten ft. of improvement depth.

The strength of the installed soil-cement grid was verified at 30 core locations selected by the engineer. From these cores, a local testing company cut 2.5"- 5.0" samples to be prepared and tested for unconfined compressive strength.

All core specimens were tested, and the results were above the specified strength requirements. The average strength was 150 psi, with 95 percent core recovery. Raito's DSM ground improvement work did not cause overstress or displacement work for the existing flood walls, a concern of the client before construction.


This project included some of the most stringent geotechnical requirements for quality control and assurance we have encountered. Raito achieved compliance with all project requirements. The New Orleans Corps District has since specified a preference for wet mix DSM, which is a testament to Raito's technique and participation in the success of this project.



Project Highlights

  • DSM was designed to prevent slide failure of the existing flood walls during the 100-year storm event. The grid-type DSM improvement system was built behind the flood walls with 40-foot-wide grids of in-situ mixed walls. The grids extended for 899 feet with an average depth of 77 feet.

  • The dry mixing method for DSM improvement was initially proposed, but Raito recommended wet mixing due to the high plasticity of clay at the bottom elevation in the project area.

  • Triple-axle DSM equipment was used to improve soils, with one DSM soil mixing rig working double shifts to meet the construction schedule.

  • DSM construction exceeded unconfined compressive strength and soil mix uniformity requirements. Design specifications required an average shear wall unconfined compressive strength of 120 psi at 28 days.





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