February 27, 2012 - Help for a Leaning Tower?

On this date in 1964, the Italian government made an announcement: please, world of engineers and architects, help us prevent the Leaning Tower of Pisa from collapsing.

Almost as soon as construction started on this grand bell tower, way back in 1173, the building started leaning one direction. When only three floors had been built, construction stopped for almost a century. When work resumed, the chief engineer decided to compensate for the visible lean by making the new stories slightly taller on the short side. In 1278, workers reached the top of the seventh floor—and the tower was leaning nearly three feet! Construction stopped again.

In 1360, builders decided to finish off the tower with an eighth and final story. Again, a cheat was used to counteract the lean—this time, the bell chamber was built with a slight slant in relation to the rest of the tower. By 1370, the structure was declared finished and declared an architectural wonder. People came from all over to admire it. Look at the six external arcades! The 200 columns! The very distinct lean!

One reason
people want to
visit the tower
is to take
advantage of
this photo op!
The tower leaned just a little more each and every year—although of course that only made people even more interested in seeing it!

In the 1500s, the top was 12 feet south of the base. In the 1800s, an architect was ordered to excavate the part of the base that had sunk into the ground—and water came up out of the ground, and the tower lurched another few inches to the south. In the 1900s, Mussolini ordered engineers to pour concrete into the foundation to reverse the tilt. But the tower leaned even more inches southward!

Recently scientists have discovered that the tower was built over the remains of an ancient river estuary, on ground filled with water and silty sand. No wonder the building has been sinking!

After the 1964 call for help, two different attempts to stabilize the building resulted in even greater leaning. Finally, in 1990, the Italian government closed the building to visitors out of safety concerns. Plastic-coated steel tendons were built around the tower, a concrete foundation with counterweights was created on the north side of the tower. These measures helped reverse a bit of the learn but were a bit “unsightly.” 

Lead counterweights, 1998.
This is what I saw when I visited Pisa.

This 2004 photo shows no cables--
when I went, there were lots of
cables!--and shows people at the
top of the tower--which wasn't allowed
when I was there.
 In 1999, engineers began to very slowly extract soil under the north side of the tower—just a gallon of soil a day—using massive steel cables to stabilize the tower during the process. By the end of 2001, 18 inches of lean was reversed, and the tower was reopened to the public.

Of course, the only time I visited the Leaning Tower of Pisa was during the 11 years it was closed! Rats!

Also on this date:

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