Lock, stock and barrel

Barnhart was contracted to remove and replace the two lower pool lock gates ‘in the dry ’ on a large ship lock in Mobile, Alabama. Each gate measured 85 feet tall, 65 feet wide and 7 feet thick (26 x 20 x 2 m), and weighed in at 360 tons (327 tonnes). Matters were further complicated by the tight time constraints on the project - just 30 days were programmed in for this phase.

Barnhart devised a solution comprising a portable, high capacity bridge crane to span the dock, and fitted with a 500 ton (454 tonne) winch. The old gates would be lowered onto a barge, which would also deliver the new ones, and throughout the lifting procedure this vessel would act as a tailing device.

These lifts presented a range of engineering and planning challenges, not least of which were the span, the weight of the load and the obstructions of the lock structure. In addition, Barnhart had just three weeks to design, fabricate and test the bridge.

New equipment developed for the project was the trolley gantry (with BCR containerised 500 ton hoist) and BCR gripper system with wheel-mounted end trucks. Barnhart also modified existing 60 foot long, 8 foot (18 x 2.4 m) deep box girders to give the required 150 foot (46 m) span.

Execution of the project involved removing each of the two lock gates by rotating them out of their hinges, before first lifting them up between the two 8 foot (2.4 m) deep trolley girders and then lowering them onto the barge. The new gates were delivered by barge and temporarily installed in the reverse of this procedure. With this complete, the lock was temporarily dammed and drained to allow the final installation and inspections.

The project was under fixed lump sum contract, which included an agreement to accept liquidated damages for exceeding scheduled outage days. Barnhart completed assembly, removal, replacement, draining procedure and permanent installation lifting within 15 days - half the originally proposed period.

In addition to its commercial and technical success, the project was outstanding from a safety viewpoint. There were no OSHA recordable incidents and no first aid incidents (throughout all phases - load test, load out, erection and execution). Daily safety meetings, pre-lift meetings and fully remotely controlled operations led to the job exceeding the Army Corps of Engineers Safety Manual requirements, resulting in Barnhart being winning the Army Corps of Engineers Annual Safety Award.