01/04/2025
Why the Tower of Pisa is leaning?
Have you ever wondered why the Tower of Pisa is leaning?
The Leaning Tower of Pisa is the bell tower of Pisa Cathedral, built in the Field of Miracles.
Its construction began in 1173 AD with the laying of a 3-meter-deep slab, upon which the walls were built. When the building reached the third floor, it was noticed that it was beginning to lean.
We are talking about a 14,500-ton tower built on 3-meter-deep foundations resting on sandy and silt soil.
After detecting the slope, the engineers of the time built the walls of the remaining floors so that the height of the floor on the most sunken side was greater than its height on the other side, thus compensating for the angle of inclination.
This tilted the tower even further due to the sinking of the foundations to a greater extent on the already sunken side than on the other due to the increased weight on that side.
Construction lasted 199 years, and the various stops in the process were one of the reasons that allowed the soil to become compacted.
The compacted clay soil has been the reason the tower hasn't collapsed, withstanding four earthquakes without toppling over. However, if left standing on that type of soil, this jewel would eventually collapse. So modern engineering was needed.
Modern engineers calculated the tower's center of gravity, and from the calculations it was concluded that the tower would collapse if a slope of more than 5.44 degrees was reached.
The tower was closed in 1990 for repairs. 361 holes, 40 meters deep, were dug, and 90 tons of concrete were injected into the ground. (That's 361 columns, each 13 stories high, "driven" into the ground.)
In foundation jargon, piles were driven under the slab. This is like placing columns that pe*****te the unstable soil layer and "drive" into the deeper, stable soil layer to keep the slab equally stable.
The earth was then removed from the least sunken side of the tower so that it would sink on that side and reduce its inclination to the original four degrees, and finally steel anchors were used to fix the tower's bases to the ground, stabilizing it.
The tower could have been left vertical, but they didn't want the tower to lose its fame and tourist value due to its leaning. After confirming that it could stand for 300 years without leaning, the tower was reopened to the public.