Fixing the Leaning Tower

The Leaning Tower of Pisa has a world famous tilt that causes it to be one of the world’s most popular tourist attractions. In 1990, the Italian government enlisted a team of engineers to stabilize the tower. Using computer models, they projected that the fatal angle, the tilt at which the tower would topple, was 5.44 degrees. At the time, the tower was tilting at 5.5 degrees! There had been many attempts over the tower’s history to right the tilt. How did engineers finally manage it?

After WWII, researchers developed tests to identify variables needed to calculate the fatal tilt, as well as fix the tilt. In 1970, engineers calculated the tower’s center of gravity. The definition of the center of gravity is an imaginary point where the total weight of the tower is assumed to be concentrated. Finding an object’s center of gravity makes it significantly easier to do mathematical calculations, such as calculating that fatal angle. With this information and emerging computer-modeling technology, engineers could estimate and model previously unknown variables such as how stiff the soil is and exactly how much excavation was necessary to prevent the towel from falling down.
In 1992, two years after the engineers figured out the angle, the team drilled diagonal tunnels to remove soil from under the non-sinking end. The structure was then counterbalanced with 600 tons of lead and anchored with steel cables. The tower now had a tilt of four degrees; engineers kept the tilt so the tower would remain a famous tourist attraction.