Hurricane Flood Wall, Westwego LA
On 29 August 2005, Hurricane Katrina made landfall, causing major damage in southwest Louisiana. Hurricane Rita followed this storm on 24 September 2005, and made landfall on the Louisiana-Texas state line. Since these storms, the U.S. government has funded projects to raise the level of protection for residence and business 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 reinforcement of flood walls for higher water events in the Westwego to Harvey area.
Downtown New Orleans flood after Katrina
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, which runs parallel to the flood wall.
In-situ soft silts and clays had variable and often high moisture contents. Variable organic content was high in approximately the first 10 ft. from the ground surface.
Raito studied the properties of the organic matter before the specified test section was started.
According to the chemical testing results, organic matter included approximately 5% Humic and Fulvic acids and 15% ignition loss.
Cementation and pozzolanic reaction of cement materials are generally blocked by these acids at 1% content. Also density of the soil cement deteriorates when ingiion loss is 10% or more.
Raito performed physical trenching to remove organic matter at shallow depths and used a unique injection system for first 10 ft. of improvement depth.
Strength of the installed soil-cement grid was verified at 30 core locations selected by the engineer. From these cores, 2.5"- 5.0" samples were cut to be prepared and tested for unconfined compressive strength by a local testing company.
All core specimens tested 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 over-stress 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 we have encountered for quality control and assurance. Raito achieved compliance with all project requirements. The New Orleans Corps District has since specified a perference for wet mix DSM, which is a testament to Raito's technique and participation in the success of this project.
Cores of in-situ DSM
3-Axis DSM Rig
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 ft. wide grids of in-situ mixed walls. The grids extended for a distance of 899 ft. with an average depth of 77ft.
- The dry mixing method of DSM improvement was proposed at the beginning, but Raito recommended wet mixing due to high plasticity 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.