Leaning Tower of Pisa is safe

Thousands of tourists visit the Leaning Tower of Pisa every year to pretend they are leaning against or supporting it. Although it’s just a photo shoot, the tilt of the tower has been a source of concern for engineers and historians for decades. Fortunately, a belfry in Italy has recently been found to be steadily rising thanks to stabilization work.

An 11-year stabilization project reduced the tower’s slope by 38 centimeters by 2001, and in the 21 years since then, the tower has straightened another 4 cm.

According to professor of geotechnics Nunziante Scqueglia of the University of Pisa, the slope of the tower has decreased, but it still fluctuates by an average of about 0.5 mm per year.

The medieval bell tower, a symbol of the power of the maritime Republic of Pisa in the Middle Ages, managed to survive at least four strong earthquakes that have occurred in the region since 1280. A 2018 study found that it was the softness of the foundation soil, which was initially responsible for the slope, that protected the tower from violent tremors.

It is assumed that the 57-meter tower began to sag after construction, which began in 1173. The reason was an error in the calculations, the foundation was only three meters deep and was located in weak, unstable soil. The foundation was softer on the south side, resulting in a lean, so the builders tried to compensate by adding eight more floors.

The floors were made shorter on one side, causing the structure to bend and lean. Construction was only completed in 1319 due to battles between Pisa and Genoa, Lucca and Florence, but these pauses gave time for the underlying soil to settle.

Fast forward to 1990, the tower was still tilted 5.5° to the south and was closed to the public for fear that it was about to collapse. After applying several different unsuccessful strategies to straighten the structure, the engineers decided to try “digging the soil”. To do this, two truckloads of earth had to be excavated from under the north side of the tower before using steel cables to raise it to a vertical position. While this was effective, the team found that the building leaned more during winter rains as the water table was higher under its north side. Therefore, they also had to dig drainage channels so that water could flow into the wells and keep the foundation stable. The project was completed in 2001.

Experts said the tower would be safe for the next 300 years. And maybe one day, the tower will one day fully straighten up.

Christina DENISYUK.

Photo: Geoff Moore/REX/Shutterstock;

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