The “Leaning Tower of Pisa” is a famous tourist attraction in Italy. However, it is not the only well-known leaning structure. From the Dancing House in the Netherlands to the Tiger Hill Pagoda in China, various leaning structures around the world astonish people. Do you know why these structures lean? And why don’t such leaning structures collapse?
Professor Mandy Korf from Delft University of Technology in the Netherlands explains that there are various reasons for leaning. In some cases, like the famous Dancing House in the Netherlands, the foundations are weak, causing buildings to lean. “Many buildings in central Amsterdam are built on wooden piles,” Korf says. According to her, wooden columns connected beneath the walls are embedded in the ground. These piles are driven nearly 12 meters deep underground, but the soil is soft, dissolvable, or sandy in nature.
Talking about the condition of the Pisa Tower, Professor Nujiante Squeglia from the University of Pisa states that the tower started leaning right from its construction. “The soil was very soft, so it began leaning from the start. It had already sunk by three to four meters,” Squeglia said. Changes humans introduce to the soil can also cause buildings to lean.
The Old Church in Delft is an example of this. “Its cause is different from that of the Pisa Tower,” Korf explains. “Since it is near a canal, digging soil for the canal caused it to lean to one side.” Changes in the underground water table can also contribute to buildings leaning. According to Korf, in some cases, the design of the building itself can create conditions for leaning. “Many houses in Amsterdam lean forward because commercial buildings were originally constructed that way,” she notes.
Dr. Korf mentions that not all leaning buildings are structurally unsafe. “For a structure to be unstable, significant cracking is necessary,” she says. In some cases, leaning buildings need to be repaired. The Pisa Tower was made somewhat upright as well. During the 20th century, the tower was leaning significantly and continuing to tilt. “At that time, the situation was very concerning,” Professor Squeglia noted. After the collapse of Italy’s Civic Tower in 1989, access to the Pisa Tower was restricted the following year.
“An approach was taken to excavate approximately 37 cubic meters of soil from the northern side of the tower,” Squeglia explained. After 11 years, the tower was reopened to visitors. According to Korf, this method of structural reinforcement was not common but specially designed for the Pisa Tower. “If a leaning building has wooden piles like those in Amsterdam, replacing them can stop the leaning process,” Korf added.
However, sometimes this can cause more damage. “If it is too tilted, straightening it out is very risky because the structure is stable in its leaning position,” she said. Regarding the impact of climate change, she stated that over 75,000 houses in the Netherlands are built on wooden piles and face risks.
The leaning of the Pisa Tower was reduced by 40 centimeters over 11 years. This work was completed in 2001. Engineers have stated that the structure is safe for the next 200 years.
