Why Doesn’t The Leaning Tower Of Pisa Fall Over?

Why Doesn’t The Leaning Tower Of Pisa Fall Over?


In 1990, the Italian government enrolled top engineers to secure Pisa's iconic Leaning Tower. Various attempts to right the tower had been made over the tower's 800-year history, but computer models showed the urgency of their situation. They projected that the tower would topple if it reached an angle of 5.44 degrees and it was currently leaning at 5.5. The tower's survival was a mystery, but the situation was obvious. They had to solve a problem that had baffled engineers for decades, and they had to do it quickly.

It's important to consider why the tower tilted in the first place in order to comprehend their condition. In the 12th century, the wealthy maritime Republic of Pisa set about turning its cathedral square into a magnificent landmark. The original church was embellished and expanded, and a massive domed baptistery was added to the plaza. Construction on a free-standing bell tower started in 1173. The builders and architects of the time were masters of their profession, but they knew very little about the land they stood on.

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Pisa gets its name from a Greek word that means "marshy field," which perfectly describes the city. Huge stone pillars called piles, which rest on Earth's solid bedrock, were used by the ancient Romans to combat similar conditions. The tower's architect, on the other hand, thought that a three-meter base would be appropriate for their relatively short construction. Unfortunately for them, the tower's southern side was already underground less than five years later. Normally, such a swaying base would be a fatal flaw. The strain from upper stories would sink the structure and fatally raise the lean if the staff added more weight.

In the 12th century, the wealthy maritime Republic of Pisa set about turning its cathedral square into a magnificent landmark. wikimediacommons

However, construction halted at the fourth story for nearly a century as Pisa descended into prolonged warfare. The soil had settled during this period, and when the building resumed in 1272, the base was slightly more stable. Staff compensated for the tower's slight tilt by raising the next few floors on the southern side under the direction of architect Giovanni di Simone. Despite this, the extra masonry caused the side to sink even further. The angle of the tilt was 1.6 degrees when they finished the seventh floor and bell chamber.

Engineers have pursued a variety of approaches to deal with the lean for decades. They dug a walkway around the base in 1838 to investigate the sunken foundation. However, removing the supporting sand made the tilt worse. The Italian Corps of Engineers injected mortar into the foundation in 1935 to reinforce it; however, the mortar was not uniformly dispersed across the foundation, causing another sudden decrease. Both of these unsuccessful attempts pushed the tower closer to the edge. Engineers couldn't pinpoint the tower's fatal angle or formulate a way to avoid it falling because they didn't know the soil composition.

Later, in the 1970s, engineers measured the curved tower's center of gravity. Engineers could model how stiff the soil was, the tower's trajectory, and the exact amount of excavation required for the tower to remain standing using this data and modern technology. In 1992, the team dug diagonal tunnels under the tower's north end to drain 38 cubic meters of dirt. The framework was then temporarily balanced out with 600 tonnes of lead ingots before being anchored with steel cables. The tower was eventually straightened to a tilt of about 4 degrees more than 6 centuries after it was built. No one wanted the tower to collapse, but they also didn't want the most iconic aspect of the landmark to be lost. Today the tower stands at 55 meters tall, and it should remain stable for at least 300 years.

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