Tetra Tech EC, Inc. (Tetra Tech) was awarded a $33.3 million contract by USACE Hurricane Protection Office (HPO) to build a hurricane risk reduction floodwall and five floodgates in New Orleans. The 18-month firm fixed price contract includes demolition, floodwall construction, and earthwork along the lakefront levee reach from the 17th Street Canal to Topaz Street. The field activities for Reach Lake Pontchartrain Vicinity 101, Phase 2 (LPV-101.2), 17th Street Canal to Topaz Street include: 

• Mobilizing
• Removing the existing floodwalls and gates on Lakeshore Drive and Lake Marina Avenue
• Constructing a temporary cofferdam at the Marina Boat Harbor
• Driving new sheet piling, H piling, and precast concrete piling along Lakeshore Drive and Lake Marina Avenue
• Relocating the existing utilities and storm drains
• Constructing new floodwalls and installing new gates along Lakeshore Drive and Lake Marina Avenue connecting to the 17th Street Canal
• Finishing the grade and installing concrete scour protection
• Replacing removed pavement and re-vegetating disturbed areas
• Demobilizing

Mobilization activities included the establishment of environmental controls, the installation of safety fencing, the staging of construction trailers and facilities (both for the project team and HPO personnel), and vibration monitoring. The project site was assessed to locate discharge points, existing drainage pathways, and overhead and buried hazards or obstacles. Hazards and obstacles were identified, protected, or removed from the area. The limits of disturbance from the work were also determined.

The following Best Management Practice for storm water control were implemented for the affected area to control the sediment during construction: 

• Structural controls were used to divert flows from exposed soils, temporarily store flows, and otherwise limit runoff and the discharge of pollutants from exposed areas of the site. Stabilization controls included silt fence barriers and diversion dikes.

Temporary flood protection consists of HESCO concertainer baskets. These modular baskets are constructed of a steel mesh framework lined with a non-woven polypropylene material. The baskets are stacked on-site in a prescribed pattern and filled with sand to form a temporary protection structure.

Prior to the construction of the new floodwall, specified portions of existing structures within the project boundaries had to be demolished. Activities included removing the streetscape and demolishing the existing floodwall, gate appurtenance, and underground pipes, storm drains, and utilities.

Portions of the existing earthen levee are being modified to accommodate subsequent work that has the potential for clearing and grubbing. Access control was set up around the work area and access was restricted to persons involved with the work. Existing structures and features that were not to be disturbed were protected from damage during the demolition process. Vibration monitoring and evaluation was conducted throughout the demolition work.

Nearly 17,000 LF of pre-stressed, pre-cast concrete piles are required at 29 monoliths in Wall Segments 1 and 5. Pile driving operations within Wall Segment 3 are intricate due to the close proximity of the pile driving to an existing apartment building and parking structure. To achieve the desired result, piles are spliced in 20-foot sections until the final depth is achieved. Work in these monoliths is being conducted concurrently, with the driving of subsequent piles being conducted during splicing of earlier piles.

Sections of new sheet pile totaling over 46,000 LF and over 85,000 LF of H-Piles will be installed to support the floodwall construction in each of the wall segments and at the gate structures. Jet grout soilcrete columns are placed for seepage protection. The grout columns are installed between two parallel rows of existing sheet piles to a depth of 40 feet. These columns replace the soil between the sheet pile with a soilcrete mass to eliminate underseepage against the 17th Street Canal sheet piles and within the parallel sets of sheet piles. A sheet pile cofferdam sufficient to prevent flooding of the work area was constructed on the east end of the project site. The sheet pile design uses the wedge-type method of developing soil pressure for estimating the external forces. The resulting temporary retaining structure has a minimum top elevation and a minimum sheet pile tip elevation to meet stability and under seepage requirements, as well as those for cut-off of recharge of strata having excess hydrostatic water levels.

Construction of the reinforced concrete floodwall is executed after all structural piling, sheet pile, and stabilization pad work has been completed for a given monolith. The 17th Street Canal to Topaz Street project is on target to be completed on schedule and within budget.

Project Highlights 

• Constructed 3,220 linear feet (LF) of new floodwall and installed five new gates along Lakeshore Drive and Lake Marina Avenue connecting to the 17th Street Canal
• Conducted in the soft muddy clay of the Lake Pontchartrain Vicinity
• Executed under an aggressive 18-month schedule