Then they poured a new concrete ring around the base of the tower, to which they connected a series of cables anchored far below the surface. Next, they placed 750 metric tons (827 tons) of lead weights on the northern side of the tower. Then, in 1989, a similarly constructed bell tower in Pavia, northern Italy, collapsed suddenly.Īrmed with a plan, workers went to the site and wrapped steel bands around the first level to prevent the stone from fracturing. None of these measures succeeded, and slowly, over the years, the structure reached an incline of 5.5 degrees. They also caused future preservation teams to be more cautious, although several engineers and masons studied the tower, proposed solutions and tried to stabilize the monument with various types of bracing and reinforcement. The tower began to lean even more precipitously. To seal the base of the tower, workers drilled a network of angled holes into the foundation and then filled them with cement grouting mixture. In 1935, engineers became worried that excess water under the foundation would weaken the landmark and accelerate its decline. These measurements revealed a startling reality: The top of the tower was moving at a rate of around 1.2 millimeters (0.05 inches) a year. Careful monitoring, however, didn't begin until 1911. Finally, between 13, workers finished the project, once again trying to correct the lean by angling the eighth story, with its bell chamber, northward.īy the time Galileo Galilei is said to have dropped a cannonball and a musket ball from the top of the tower in the late 16th century, it had moved about 3 degrees off vertical. The rate of incline was sharpest during the early part of the 14th century, although this didn't dissuade town officials or the tower designers from moving forward with construction. Unfortunately, the building continued to settle, sometimes at an alarming rate. Engineers tried to make another adjustment, this time in the fifth story, only to have their work interrupted once again in 1278 with just seven stories completed. Soil under the foundation continued to subside unevenly, and by the time work resumed in 1272, the tower tilted to the south - the direction it still leans today. Engineers now believe the Leaning Tower of Pisa will remain stable for some 200 years, barring an earthquake or other unpredictable disaster.The tower sat unfinished for nearly 100 years, but it wasn't done moving. The straightening continued after the tower reopened in 2001, and in 2008 sensors showed the subsiding motion had stopped, after a total improvement of some 19 inches. That year, the monument was closed to visitors and the bells removed as engineers started extensive reparations to stabilize it.īy siphoning earth from beneath and adding counterweights to the tower’s north end, they were able to reduce the lean to 13.5 feet, or 4.0 degrees from perpendicular. By 1990, it was leaning 5.5 degrees (or some 15 feet) from the perpendicular–the most extreme angle yet. Despite various attempts to reinforce it, Pisa’s tower continued to subside at a rate of some 0.05 inches per year, placing it in increasing danger of collapse. The tower was officially completed around 1370, but its lean only increased over the next six centuries, becoming an integral part of the monument’s quirky appeal. When construction resumed, chief engineer Giovanni di Simone tried to compensate for the lean by adding extra masonry to the short side, but the additional weight caused the structure to tilt even further. This delay allowed the foundation to settle further, likely prevented the bell tower’s premature collapse. Shortly after that, war broke out between Pisa and Genoa, another Italian city-state, halting construction for nearly a century. As a result, the structure had begun to tilt visibly toward the south. By the time builders had finished the third of eight planned stories about five years later, the tower’s foundation had begun to settle unevenly on the ground beneath it, a dense mixture of clay, sand and shells. In 1173, construction began on a white marble bell tower for the cathedral complex in Pisa, located between the Arno and Serchio rivers in Tuscany, central Italy. The so-called Leaning Tower of Pisa is one of the most famous buildings in the world, although maybe not for the reasons its original architects would have wanted. Pick any day in the Piazza del Duomo in the Italian city of Pisa, and you will undoubtedly spot a bunch of tourists posing for the same photo: hands outstretched towards the cathedral’s conspicuously tilting bell tower, as if they are supporting it with their sheer strength.
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