And will the Pisan tower ever fall?
Oh, these architectural features. Take, for example, the drawback of the Pizan tower who made it popular. She spent almost 840 years in an inclined state and naturally asking me to ask if gravity will ever win? In fact, the famous structure is in jeopardy from the moment when its very first stone was laid.
From the first stone everything did not work out ..
The Pizan Tower tower was tilted shortly after the start of construction in 1173. The builders only reached the third floor, when the base began to seriously move out on soft grounds consisting of dirt, sand and clay. The workers tried to compensate for this by making the columns and arches of the third floor slightly higher, but they did not stop the construction, so as not to deprive themselves of the work. When they built the fourth floor, unrest began and construction stopped.
The tower “sat” for almost 100 years, but did not stop moving. The soil under the foundation continued to weaken unevenly, and by the time of resumption of work in 1272, the tower leaned south. Engineers tried to make another adjustment, but this time at the level of the fifth floor. And their work was also interrupted, this time during the construction of the seventh floor.
Unfortunately, the building continued to settle, sometimes at a threatening speed. The speed of inclination was very high in the first half of the 14th century, although this did not dissuade city officials and tower designers to move forward and continue to build. Finally, between 1360 and 1370, the project was completed. Once again trying to fix the work of the first builders, on the eighth floor they shifted the bell tower to the north.
By the time Galileo Galileo, as they say, threw away the cannon core and a musket charge from the upper part of the tower at the end of the 16th century, the Pisa tower had already stood about 3 degrees. Thorough monitoring, however, did not do until 1911. Measurements have revealed a sad reality. The upper part of the tower is tilted by approximately 1.2 millimeters per year.
Damn lump.
In 1935, engineers were worried that excess water under the foundation would accelerate the fall of the tower. To compact the base, the workers drilled a network of inclined holes in the foundation, and then filled them with a cement mixture. They only aggravated the problem. The tower began to advance even more rapidly. This stimulated the subsequent teams that worked with the project to be more careful. And many tried to come up with measures and ways to stabilize the monument with various types of fasteners and reinforcement.
And then the tower collapsed.
But not one of the attempts was successful, and slowly, for many years, the structure of the Oshedlya has already reached 5.5 degree tilt. Then, in 1989, the similar structure – the bell tower in Pavia (Italy) suddenly fell.
Officials began to worry so much because of the tower in Pisa that they closed the monument to the public. A year later, they rallied together and created an international team that was supposed to save the tower.
The right way.
John Berland, a specialist in soil mechanics from the Imperial College in London, was one of the key members of the team. He thought that it was worth extracting the soil from under the northern base, and this would pull the tower back vertically. To check the hunch, computer modeling was carried out. After analyzing the data, the group decided that such an option is really possible.
Armed with the plan, the workers wrapped the steel stripes around the first level to prevent damage to the stone. The reconstruction of the building is not a simple matter. Then they placed 827 tons of lead weights on the north side of the tower. After that, they enveloped a new concrete ring around the base of the tower, to which they attached to Seryoye cables fixed underground. Finally, using a drill of 200 millimeters, they began to make holes for the foundation. Every time they took out the drill, they took a small part of the soil – from 15 to 20 liters. This is the pressure applied by cables pulled the tower in the direction opposite to its tilt. They repeated this in 41 different places for several years.
In 2001, the team reduced the tower roll by 44 centimeters. This was enough to assure officials that the monument can be opened again for the public. Even when the drilling was stopped, the tower continued to straighten up until in May 2008 the sensors stopped detecting movements. By that time, the tower had lost another 4 centimeters of inclination and was no longer in a state of dangerous inclination.
And yet.
The actions taken by Berland and his team theoretically, can stabilize the structure constantly. The real threat is now emanating from the masonry itself, especially the material at the bottom of the building. If any masonry is violated, then the tower can collapse. And even a slight earthquake in the region can have destructive consequences.
Despite these potential problems, engineers expect the structure to be in stability for at least another 200 years. By that time, another intervention may be required, but technologies are available that can strengthen and improve the Pizan tower for another 800 years.