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A momentous move, at an inch a minute

Cape Hatteras Light embarks on journey to escape the sea

June 15, 1999|By Frank D. Roylance | Frank D. Roylance,SUN STAFF

In April, workers began cutting between the two bottom plinths at the base of the lighthouse, using a diamond-studded cable saw 3/8-inch thick. As the cut deepened, workers cut away at the bottom layer of stone -- two feet at a time -- and replaced it with shoring towers set on a mat of steel beams.

By mid-May, the cutting was complete, and the lighthouse rested entirely on the shoring. The team then began sliding welded double steel I-beams between the shoring towers. The 70-foot-wide beam system contains 100 built-in hydraulic jacks, all tied into a single control panel.

After a second layer of steel beams was inserted crosswise to the first, and clamped to it, the entire steel frame was jacked up to the granite bottom of the lighthouse.

As the jacks and beams took up the 4,400-ton weight of the lighthouse, the old beacon began to float on what amounts to a carefully controlled pool of hydraulic oil. The jacks are linked in three wedge-shaped zones, forming a three-point plane that Matyiko can manipulate from his panel.

The lighthouse has been laced with electronic sensors. Some will signal changes as small as one-hundredth of an inch in the expansion cracks that sunshine and cold sea air have opened in the brick over the years. Others will monitor the weather, any shape changes in the brick tubes, and any tilt.

"We can go a foot out of level at the base, 3 at the top," Matyiko said. "But we're within 3 or 4 inches all the time, and we can correct it at any time."

If his dials and sensors report any loss of oil pressure, or unwanted tilt during the move, he can adjust the hydraulics to stabilize the system.

"It moves one inch a minute," he said. "When you're inching along like that, you have a lot of time to figure out what's happening in front of you."

While the Hatteras light was being cut and lifted, workers cleared the 2,900-foot "move corridor," dug out any organic matter buried there, compacted and leveled the sand and soil. It was then covered by gravel and compacted again.

Last week, Matyiko began installing the Hilman roller dollies on which the lighthouse will move. Each is 2 feet long and 1 foot wide and contains a belt of rollers arranged like a tank tread. Each dolly can support 100 tons, but on this job will bear only 44.

The lighthouse will roll on hardened steel rails laid across 70-foot-square mats of 10-inch-high welded steel beams. The mats will be picked up and leapfrogged ahead of the lighthouse as it travels.

Propulsion will come from another set of hydraulic jacks. Set behind the lighthouse, they will push the steel frame five feet at a time.

A person riding inside the lighthouse would not detect any motion, Matyiko said. "You would almost have to stand something up in front of it -- pushing little soldiers over -- to monitor the movement."

After its arrival at the new site, the lighthouse will be lowered onto a checkerboard of precast concrete pads. The spaces between the squares are there to allow the removal of the steel beams from beneath the lighthouse. Once the beams are gone, the spaces will be filled with more concrete. The new base will then be buried, and the lighthouse's original granite plinths restored.

The move of the Cape Hatteras Lighthouse may be the slowest historic drama ever staged, and the most audacious. But engineers don't regard it as tremendously risky.

"There's a lot of safety factors being put into this," said Carl A. Tuxill, executive administrator of the International Association of Structural Movers.

"It's a high-publicity situation, and such a highly esteemed public building that they're leaning over backward to make it safer than usual," he said.

Said Matyiko: "Everything's gone perfect so far. We've just gotta stay on it and keep it that way."

Information and pictures are available at www.nps.gov/caha.

Pub Date: 6/15/99

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