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Inner Harbor Navigational Canal (IHNC) Lock Replacement, New Orleans

Photo: Ben C Gerwick / COWI
Aerial view of existing lock and canal, New Orleans.
The United States Army Corps of Engineers needed to replace an outmoded shallow-draft lock with a deep-draft, ship lock. COWI North America relied on its success in transferring offshore marine techniques to inland waterways at Braddock Dam to hone an innovative design.

Working with engineers URS, COWI MARINE North America began the final design services for the Inner Harbor Navigation Canal (IHNC) Lock Replacement in New Orleans, USA, in 2002.

This design involves the flotation and installation of the lock in five modules (two sector gate modules, GM1 and GM5, and three chamber modules, CM2, CM3, and CM4) which will be ballasted onto driven piles at the lock site.

During the course of design, CM2 and CM4 underwent numerous changes. For a September 2004 study, COWI MARINE North America compared two options for shells constructed in the dry and floated to the lock site.

Steel bulkheads

The preferred, shallow draft option allowed the permanent shell, from reference elevation -52.0' to -19.75', to be floated to the site with an average draft of 21'-3"; this option required reusable, temporary steel bulkheads around the shell perimeter from reference El. -19.75' to El. +6.0'.

The deep draft option allowed the full height shell (from El. -52.0' to El. +23.0') to be built in a deeper graving site then floated to the lock site with a 29'-10" draft. USACE N.O.D. selected the shallow draft option with modifications.

The modified shallow draft option (25'-9" draft) was developed for the Design Memorandum (DM)-level 100% submittal. Instead of full-perimeter, temporary, steel bulkheads to El. +6.0', the refined design relies, for the most part, on heavily-reinforced, slender, concrete walls that will be incorporated into the permanent structure.

Reinforced concrete

The CM shells will be constructed of reinforced concrete at a graving site away from the lock site. Internal compartments and temporary bulkheads and bracing, to block off the chamber space, will allow each shell to float when the graving site is intensionally flooded and opened to the waterway.

Tugs will tow the shell to the lock site, passing beneath two bridges with limited clearances and drafts. The shell will be positioned over previously installed driven piles. Ballast concrete will then be placed in the dry, internal cells over the culverts, in the lock floor, and then in the lock walls.

As the concrete filling proceeds, the draft of the CM shell will increase from 26 feet to 46 feet. Sand ballast will be added in the lock chamber to bring the shell into contact with landing piles and prevent it from re-floating if the water depth increases during construction (up to three feet).

COWI MARINE'S focus

The CM will be attached to uplift-resisting tension piles. Three feet of concrete will be placed beneath the shell by tremie pipe, connecting it to the remaining piles. The upper lock walls (from elevation +6'-0" to +23'-0") will be formed and cast in concrete. The sand ballast and temporary bulkheads and bracing can then be removed.

COWI MARINE North America's focus was on controlling construction complexity and structural weight in a lower cost structure with superior durability problems.

LAST UPDATED: 18.12.2017