Why Some of The World's Most Famous Towers Lean

Why Some of The World's Most Famous Towers Lean

Like many of the leaning towers seen today, the most famous leaning tower in the world - the Tower of Pisa, wasn't intentionally designed to be a leaning tower. It was designed to be built vertically but instead it started leaning in its construction in 1173. This article explores the reasons why towers lean and offers insight to ways that towers are restored back to a straight position. 

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Despite being highly visited tourist attractions, the slanted appearance of a leaning tower gives most people the impression that the tower would not be safe to reside in. The safety of the building isn't of a concern when it comes to a leaning tower since the leaning of the tower isn't due to an architectural flaw. Rather it is caused by geotechnics - the foundation the building is built upon. 

image © Umschauen // Tower of Church of Suurhusen

image © Umschauen // Tower of Church of Suurhusen

According to the Oxford Dictionary, Geotechnics is "the branch of civil engineering concerned with the study and modification of soil and rocks." When analyzing the ground, most of the causes for a leaning tower are soft or weak spots which weren't detected during the plotting of the land. It's also possible that the investigator of the land did not search it deep enough and therefore missed unexpected geological faults in the ground. Through an analysis of the foundation, an individual can discover the cause of the lean and learn ways to fix the problem.  

image © Gavrilov S.A. // The Leaning Tower of Akinfiy Demidov

image © Gavrilov S.A. // The Leaning Tower of Akinfiy Demidov

If the ground is not at fault, there are other possible reasons such as design issues, the type of foundation chosen, construction control, or supervision of the site. While many want to accuse mother nature for the error, the cause can be traced back to being a human error for not conducting a proper ground investigation before beginning construction. 

image © Michael // The Yunyan Pagoda

image © Michael // The Yunyan Pagoda

Although there are multiple leaning towers in the world, they are relatively rare. This could be because some of them have already been straightened. In order to straighten a tower, the process is vigorous and includes an abundance of finances to investigate the ground around the tower and the implications of what has been happening over time. Once the cause has been found, eventually a solution can be made to straighten the tower.

image © Roberto La Forgia

image © Roberto La Forgia

Some of the most common solutions is compensation grouting or injecting grouting into the ground to attempt to lift one side of the building compared to the other. This process requires precision and uses very specialized equipment.  It is more time consuming than the alternative method which is cutting the building at its foundation level and inserting jacks to jack the building straight. 

pictured above is the Tower of Pisa prior to 1999 on the left and restored on the right.

pictured above is the Tower of Pisa prior to 1999 on the left and restored on the right.

While some towers can use the techniques listed above to make them straighten out, in the instance of the Leaning Tower of Pisa, it underwent an 11-year rehabilitation period that began in 1992. The first attempt to save the tower consisted of encircling the first floor with 18 steel cables as a temporary structural reinforcement measure. Next there was construction completed underground which saw ancient blocks of stone conglomerate being extracted. The blocks were then substituted with a girder and reinforced concrete which the had steel cables that kept the tower anchored. The final construction was completed in 1999 when the earth beneath the tower's foundation was excavated and removed. It proved to be most successful as the tower's lean declined by 2.5cm. 


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Sources: CNN, CNN Style

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