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| Reaching Out. Ramp can move 29 ft down to water level to accommodate roll-on cargo. |
The manually controlled ramp lowers from a deck elevation of 29 ft to water level for roll-on cargo, using a hydraulic cylinder to wind up or release chains to place it at the appropriate level. It will ease delivery of supplies to the Navys San Nicolas Island base in Californias Channel Islands, about 70 miles southwest of Los Angeles.
Before the structure was built, consistent 2-ft-high waves and winds averaging 40 knots made delivering supplies dicey. They had to be offloaded onto the beach using a pontoon structure. "Sometimes the only window when barges could land was midnight," says Mark Foster, Navy project engineer.
Nothing like the $11.5-million project has ever been built before, engineers say. The design-build contract for the pier, mooring systems and ramp was awarded in 2002 to Nova Group, Napa, Calif., by the Southwest Division, Naval Facilities Engineering Command, San Diego, assisted by the NAVAIR Weapons Division and the Naval Facilities Engineering Service Center. "We approached this project as if it was being built in the middle of the ocean," says John F. Jones, federal heavy structures manager for San Francisco-based Winzler & Kelly Consulting Engineers, Novas design partner.
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| Barging In. Modules were fabricated in Napa. |
Controlling the movement of barges so they do not surge in and out was crucial, says Jones. To accomplish this, Nova installed 62 prestressed concrete composite piles, each 24 in. diameter with 12-in.-dia steel pipes in the center. Instead of driving them, crews extended the drill hammer stem through the pipes. When the hammer reaches a 1Ú8--in. lip at the bottom of the pipe, the drill is activated and the teeth are extended about 6 in. into the ground. As the drill works, sand is shot out of the way using air pressure and a cable holding the pile slowly releases, dropping it into position 30 ft deep. "It is a much more precise way of placing piles," says Fox. High-pressure grout holds the piles into place.
Crews built the 173.9-ft long x 22-ft wide x 6-ft deep steel-plate ramp in four 80,000 lb sections in Napa and towed them into place. Jones says the barge-like box structure has no sharp edges, to enhance corrosion protection. They can be towed to a drydock for repairs.
Once the first pier was in place, crews began building the trestle work platform, but discovered a faultline, says Nova project manager Dan Fox. Although borings from near the shore had found solid rock, sandstone encountered farther out turned to mush when drilling began. "We had to redesign the project to go down another 20 ft until we hit solid rock," Fox says. A total of 34 rock anchors were added and the work continued after a 400-day delay.
"The biggest challenge was simple logistics," says Fox. More than 3,000 cu yd of concrete, 15 barges of aggregate and 30 employees working 10-day shifts had to be ferried to the island from Long Beach. Up to 1,000 elephant seals also had to be shooed from the beach by environmentalists. The barge operator was brought in early to test pier stability.
Base operations also posed a challenge. "Sometimes, we had to be sequestered while they did operations," says Fox. The island hosts classified defense activities, such as operation of a remote-controlled ship and instrumentation that supports ballistic missile and satellite launches for the Navy.
(Photos courtesy of Nova Group Inc.)
orking around 6-ft rogue waves, stubborn seals and an unexpected fault line, crews are completing an adjustable 460-ft-long pier, mooring system and mechanical ramp for the U.S. Navy that is the first of its kind.
