Righting One Wrong Tower.(leaning tower of Pisa)(Brief Article)

For much of the last decade, Italy's leaning tower of Pisa was a huge construction site. Crews piled 900 tons of lead bricks around the tower's base. More recently, they drilled holes beneath the tower, inserted pipes and sucked out 70 tons of soil to be carted away by a fleet of dump trucks. As a safety net in case the tower toppled during this operation, restorers encircled its midsection with a four- centimeter-thick cable. Then, a few weeks ago, they packed up their earth-moving machines and went home. The latest effort to keep the 800- year-old tower from becoming yet another of Italy's many ruins had come to a close. And, with any luck, so ends a series of engineering gaffes and accidents that stretch back over most of the second millennium. On June 16, the engineers will turn it over to the city of Pisa at a gala affair, followed the next day by the annual celebration of Pisa's patron saint Ranier. Candles will be floated down the River Arno, and tenor Andrea Bocelli will give an open-air concert. Once and for all-- fingers crossed--the leaning tower has been righted.

Well, not quite. John Burland, the soil-mechanics professor from England who led the effort to save the tower, has managed to reduce the distance that the tower's top leans over its base by about half a meter, so that it now overhangs by a mere three and a half meters. That puts the tower's tilt at a safe five degrees, as opposed to the treacherous 5.5 degrees it had hit when the city of Pisa hired Burland in 1989. The fix required raising the north side of the tower's base by four meters. (If that doesn't sound impressive, keep in mind that the tower weighs 14,700 metric tons.) It's now as straight as it was in 1810--that is, stable enough to stand but not so straight as to entirely lose its tilt, which has so endeared it to tourists. Burland is happy enough that it's standing at all. "That's extremely good news," he says. "It was very close to falling over on many occasions."

Almost as soon as construction on the tower began in 1173, its marble foundation began to sink into the soggy clay on Pisa's Campo dei Miracoli (Field of Miracles), the site of a buried riverbed. Burland likens the building of the tower to a child's carelessly stacking toy blocks on a carpet. "It was built on very soft ground and is at a very critical height," he says. The 13-member commission to save the tower, which Burland headed, meticulously fed all the data it could into a computer, but the answer was always the same: if a tower built at that height of those materials on ground of just that sponginess were to lean as much as 5.4 degrees, ...