Foundation is made of Sterner Stuff !
A tourist with giant hat flashes a big smile while bearing the entire weight of the Tower of Pisa and click! Here is a photograph to cherish for life. If you are wondering why the tourist from another country needs to travel these miles to support this iconic structure, the answer is very simple. As you may have guessed from the title the Tower of Pisa’s foundation is not doing a good job. In fact we recognise it as the Leaning Tower of Pisa.
Case studies are one of the best ways of learning how to do things better and the Leaning tower of Pisa has been a good contribution as an example to geotechnical engineers. In the first year of my bachelor degree, we were posed with a question, “Why is the Leaning Tower of Pisa leaning?” We had no answer then. We were aptly answered with the following explanation: The soil under the foundation is not strong enough to carry the weight of the building.
The details are as follows, the foundations is about 3 metres thick on a soft silty soil. Ideally the weight of the building should have consolidated the soil and the leaning tower would not have been leaning so much! There are multiple factors affecting a substructure. An unpredictable one is water table. Due to the fluctuating water table with a higher affinity to the north of the Tower, the Tower began tilting towards the South. Hence uniform settlement of the soil was not possible.
The Tower has been slanting at an alarming angle of 5 degrees from the perpendicular for about 800 years now! To fix the inclination problem, a restoration project led by John Burland, Emeritus Professor and Senior Research Investigator at the Department of Civil and Environmental Engineering of Imperial College London and 13 experts set to work in 1990. The basic solution was to reinforce the soil. This project took 10 years to complete and a total of 30 million EUR! Hefty price for straightening out!
Here are the specifics: Soil extraction was performed. About 2 lorry loads of soil was extracted. A series of tunnels were dug out for this purpose. This was done to reduce the building’s stress on the masonry and for the foundation to align by itself while steel cables pulled the building to the original position. Digging wells and draining water from them to keep the water table consistent at the location was one of its phases. Modern day reinforcement by 15 metre concrete pillars in the ground was erected.
This project successfully decreased the inclination by one degree and 50 cms, turning back time for the Leaning Tower of Pisa by 200 years. When its inclination was 4 degrees. The leaning Tower has been leaning again by 2.5 cms but engineers have confirmed that the monument is actually going to be safe for another 200 years. Also by popular vote people believe that, “The tower was born leaning so it should remain left leaning.” Projects to erect the Tower will only begin if it threatens the safety of people and place around. So for the next 200 years, people from all over the world can continue clicking their brave pictures of physically supporting the Tower!
References:
1) https://leaningtowerpisa.com/facts/how/how-pisa-leaning-tower-was-stabilized
3) https://madridengineering.com/case-study-the-leaning-tower-of-pisa/
4) Google Images