Lean In…Literally

The Leaning Tower of Pisa is symbol of Italy, a glorious structure that conjures images of rolling Tuscan fields, freshly baked pizza, and miles and miles of vineyards.

And yet, in reality, it is a historical landmark only still standing because of its home country’s humbleness and the grit and determination of a multi-national team of scientists and engineers.

Photo Courtesy of Jennifer Wright, 2008

The Leaning Tower of Pisa is actually the bell tower of the Pisa Cathedral. Construction began in August of 1173 with a 3 meter foundation of heavy white marble on soft, weak soil–a mixture of sand and shells, due to an ancient river estuary directly beneath the tower. By the time builders reached the third story five years later, the structure had already started to settle, albeit with a very noticeable lean. The stones were simply too heavy for the poor soil, a design flaw architects hadn’t anticipated.

It was only the outbreak of war between Pisa and Genoa, as well as subsequent skirmishes with Lucca and Florence, that saved the tower. Because of these battles, construction was halted for nearly a century, giving the soil a chance to solidify somewhat and preventing the structure from collapsing completely.

When construction resumed in 13th century, rather than tearing it down and starting over, engineers instead decided to compensate for the lean by adding extra masonry to the short side to add support as well as building upper floors with one side taller than the other. The result, however, was actually an added tilt as well as a curve in the general shape. The tower was finally completed in 1372 and soon became known as an architectural wonder, with people from all over the world coming to marvel at its beauty and it quirk.

But it soon became apparent the lean was no mere whimsy.

Engineers soon discovered that the tower’s tilt was actually increasing, subsiding at a rate of some 0.05 inches per year. Despite various attempts at stabilization from some of Italy’s top minds, the structure continued its perilous journey towards total collapse.

By the 1960s, the top of the tower was hanging over seventeen feet south of its base. The landmark was becoming a danger to Pisa, to the surrounding historic buildings, and to itself. On February 27, 1964, Italy officially sent up the white flag, asking for the world for any ideas on how to save its leaning landmark.

A multinational task force of engineers, mathematicians, and historians gathered in the Azores to discuss theories and methods of stabilizing the structure. As a temporary reprieve until a more permeant solution could be solidified, 800 tons of lead counterweights were affixed to the raised end of the base.

A series of trial and error resolutions ensued, including several drilling attempts which only resulted in further leans. In 1990, the Italian government closed the Leaning Tower’s doors to the public out of safety concerns. The bells were removed to relieve some weight, and cables were cinched around the third level and anchored several hundred feet away.

It was time for more drastic measures.

It was decided that the best way to prevent collapse was to remove soil beneath the raised end, thereby reducing the tilt. In order to temporarily stabilize the building during excavation, plastic-coated steel tendons were built around the tower. Soil was removed from the north side of the tower slowly, no more than a gallon or two each day, and a massive cable harness held the tower in place for safety. Careful, methodical digging resulted in an eighteen inch reduction in tilt and–for the first time in its history–the Leaning Tower of Pisa was no longer moving.

It reopened to the public in December 2001.

Just in time for me to visit and do the stereotypical tourist pose.

Photo Courtesy of Jennifer Wright, 2008

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s