Efforts to hold Leaning Tower of Pisa going better than expected: ScienceAlert

Take a look at Italy’s Leaning Tower of Pisa and one question comes to mind: how close is the tipping over?

For decades upon centuries, engineers, historians and onlookers have been holding their collective breath over the fate of the iconic bell tower, which has weathered four earthquakes and sways back and forth but somehow still stands with that namesake tilt.

It is not without some clever intervention that the tower has avoided a rendezvous with gravity. In fact, before it was even finished, engineers struggled to get the structure back up.

We can all breathe a sigh of relief now, thanks to the steeple’s latest survey, which has found its health to be much better than predicted. The tower has crept upright by about 4 centimeters (1.6 in) in the 21 years since the last stabilization works were carried out.

The survey was carried out by a team of geotechnical engineers and funded by Opera Primaziale Pisana (O₽A), a non-profit organization established to oversee construction work to preserve the historic site.

“Given that it is an 850-year-old patient with a slope of about five meters and a subsidence of more than three meters, the state of health of the Leaning Tower of Pisa is excellent,” an O₽A representative told Italy’s National Associated Press. Agency (ANSA) earlier this month.

Construction of the Leaning Tower of Pisa began in 1174, and within a few years – after its first steps were actually built – it was obvious that something was wrong. Its shallow foundations were built on an unstable base of mud, sand and clay that was softer on the south side.

The engineers tried to correct the slope as they went, making the upper floors taller on one side than the other, resulting in what you might say is a wonderful building that is curved as well as slanted.

For many years, as its tilt increased, engineers tried to secure the eight-story tower, sometimes exacerbating the problem. By the 1990s, the Leaning Tower of Pisa was no closer to solid ground, leaning 5.5 degrees to the south, just beyond the point at which engineers thought the tower would collapse.

Uncropped 3D laser scan image of the Leaning Tower of Pisa as it appeared in the 1990s at the then 5 degree tilt.
Laser scan of the Leaning Tower of Pisa. (CyArk/Wikimedia Commons/CC BY-SA 4.0)

Shortly thereafter, the tower was closed to the public and the Italian government recruited a team of experts, chaired by a civil engineer Michele Jamiolkowski, to learn how to save it. They considered injecting cement under the tower, but decided it was too dangerous and instead attempted to anchor the north side down with 900 tons (816 metric tons) of lead to compensate for the sunken south.

When that didn’t work, they scooped up dirt from under the north side of the tower. Slowly, it began to rise – and spin. Anyone who has played a game of gravity-defying Jenga would know how terrifying this would be.

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The long-term stabilization work was finally completed in 2001, after which the tower had straightened about 40cm and now leans just 4 degrees – still twice the original lean of the building when construction was completed in 1350.

In 2013, researchers from Australia’s national science agency, CSIRO, also mapped every corner of the tower using 3D scanners, creating some eerie digital reconstructions of the tower that could be used should the building ever need repair.

A twist, we hope it won’t happen. The tower now wobbles ever so slightly, oscillating on average about half a thousand years, according to geotechnical engineer Nunziante Squeglia, professor of geotechnical engineering at the University of Pisa, who is part of the monitoring team.

“Although what counts the most is the stability of the steeple, which is better than expected,” Squeglia told ANSA.

In a country steeped in antiquity, Italy’s Leaning Tower of Pisa isn’t the only historical figure under close scrutiny for fear of collapse. Scientists have been watching for centuries for cracks in the ankles of Michelangelo’s David that could bring down the world’s most perfect statue, an effort that intensified when a 2014 paper found that a slight 5-degree tilt has already caused damage and could eventually lead to disaster failure. Earthquakes that same year did little to ease tensions.

While David’s fate is uncertain, fortunately the Leaning Tower of Pisa should be safe for at least the next 300 years and perhaps more, experts say. Some engineers even believe that restoration efforts could be so successful that the infamous tower may one day be fixed.

Ironically, the research shows that the same soft soils beneath the tower’s foundation that produced its characteristic lean may actually provide some protection against earthquakes, giving the structure a longer, less destructive period of natural vibration if it sways.

So perhaps a better question to ask ourselves is: will the Leaning Tower of Pisa ever stand? And what will happen after his name?

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