leaning tower of Pisa Leaning Tower of Pisa

The Leaning Tower of Pisa stands in the context of the wonderful Square of Miracles (a world heritage site since 1987) with its inclination of approximately 4 degrees and with its impression of falling down from one moment to the next stirs up the interest of thousands of onlookers, who delight every year remaining fascinated by oddities and weirdness of one of the most beautiful Monument in the world.

When thinking to Pisa, there is an immediate link to the famous leaning tower.

The monument assumed importance over the centuries thanks to its pronounced slope that made worry and at the same time caught the attention of numerous experts and simple tourists; the Tower (Steeple of the Cathedral of Santa Maria Assunta in Pisa Miracle's Square) is 56 meters tall and consists of 8 floors and approximately 300 steps.

It has been proposed as one of the 7 Wonders of the modern world!

leaning tower of Pisa Leaning Tower of Pisa

The construction work of the Tower of Pisa began in 1173, but because of many vicissitudes they ended many years later in 1350.

The leaning tower of Pisa, rises on a clay and sandy soil, the sinking of the underlying soil and the resulting tilting occurred since the construction on the 3rd floor so that the works had to be suspended and then started again years later, building the future plans with a bend in the opposite direction to the slope.

It is thought that the original project may be attributed to the architect Diotisalvi, who at the same time was building the Baptistery, but other theories of scholars give this fatherhood to other famous Sculptors or Architects of the time such as Bonanno Pisano.

The construction was resumed and suspended several times over the years, it carried on until in 1350 under the expert control of Giovanni di Simone and Giovanni Pisano, reaching a height of about 56 metres and a weight of 14,523 tons.
In an attempt to straighten the Tower, the following floors were erected with a tendency to sag in the opposite direction to the original slope, always managing to keep the monument in equilibrium because the vertical line passing through the centre of gravity falls within the base.

bell leaning tower of Pisa Leaning Tower of Pisa bells

The floors are 8, surrounded by a small loggia with round arches, which reflect the facade motive of the Cathedral, and, since the tower is the Steeple, were placed 7 bells in "Belfry" (top floor of the Tower):
Assunta (the biggest and heaviest), Crocifisso, San Ranieri, Dal Pozzo, Pasquereccia, Terza, Vespruccio: these are the names of the bells that still today ring before masses in the Cathedral and at midday through an electronic system. Once each of them was used to sign the liturgical moments of the day.

Pasquareccia Bell, the oldest one, for example rang for Easter....
instead the San Ranieri Bell was used to notify the death of traitors (it is said that it rang also on the death of count Ugolino), originally called Justice was placed in the homonymous Palazzo.

The structure of the Steeple consists of two rooms:
one at the base of the Tower, known as the fish Room, as inside it had a bas-relief depicting a fish; it has no ceiling being concretely the cable of the Steeple; and the other one is the Belfry, located on the seventh ring, bounded by the walls of the upper walkway, at open air, while at the centre, through an opening, it is possible to see the ground floor of the tower. To reach to the top, one must follow three flight of stairs; one is uninterrupted and goes from the base until the sixth ring, where one exits outside, another smaller staircase leads from the sixth to the seventh ring and finally an even smaller one, a spiral staircase, leads from the seventh ring to the top.

leaning tower of Pisa Leaning Tower of Pisa entrance

"The tower that hangs, that hangs, and never will come down..."
So says a Pisan historical jingle... but will it be true?

Over the centuries, despite the increase of the slope of the Tower, there have been temporary periods of stability or reduction, and many people were interested in solving the problem!
During the 19th century some soil analysis, taken during restoration work, showed the presence of a large amount of underground water which made the soil saggy. The architect Alexander Gherardesca in 1838, following the renovation of the Steeple, had the task of bringing to light all the first order of the monument, caved in the soil because of the raising of the ground over centuries. Therefore it was sought to suck the water with pumps, but this caused the subsidence phenomenon, i.e. a vertical drop of the earth's surface which accentuated the slope of the Tower!

In 1908 a "Commission for the study of the conditions of the leaning tower of Pisa was established by the Minister of education, and in 1935 the engineer Giovanni Girometti intervened to seal the foundations by cement injections (about 93 tons) and waterproofing all the surrounding basin. The cement injections were made through 391 oblique holes at the base of the cylinder. The works carried on with the removal of floor slabs to lay a "floor screed" of reinforced concrete and a superimposed layer, creating an elastic joint of these gauges with the base of the Steeple.

The working didn't lead to desired results, indeed the slope increased further.
In the following decades, the increasing of the slope was such to think of its possible collapse, so in 1973 it was designed a compensation reticular work involving the application of a tubular reticulum on the monument as a counterweight.

More "projects" were proposed to the Commission that examined the most suitable applying a new solution to the problem:
-The project "KONOIKE" transformed the physical properties of soil under the tower and around the foundations of the steeple, by mixing through particular equipment the soil with cement-suspension and special inorganic chemicals, in a continuous and uniform way

The collapse of the Steeple( Torre Civica) of Pavia in 1989 put under observation the leaning tower of Pisa that in 1990, considering a " critical situation", closed the access to the public and the Committee preparing a consolidation project.
In 1993 the slope of the Steeple reached 4.5 degrees and the fear of a concrete collapse of the structure becomes high.

In a decade of work, the slope of the Steeple is reduced through circling of some floors, temporary application of steel rods and lead counterweights (up to 900 tons) and later under-soil excavation. Moreover it is also consolidated the base allowing, according to experts, to maintain a security regime of the tower for at least three centuries, allowing the access to new visitors.

The slope was reduced by 0.5 degrees and was blocked the risk of instability, except small and occasional movements due to seasonal changes in temperature and groundwater levels.
In the basement were placed sensors to measure these variations and it was observed that over time the slope still tents to improve.
The tower was reopened to the public at the end of 2001.

The merits of the success of the operation are related to Michele Jamiolkowski, Professor at the Politecnico of Torino and President of the International Committee for the preservation of the leaning tower of Pisa from 1990 to 2001, to Carlo Viggiani, professor in the Department of geotechnical engineering at the University of Naples "Federico II" and to the President of the International Committee for the conservation of monuments and historic sites and J. B. Burland, Professor of the Department of Civil Engineering at Imperial College of London.

The experts thought that further developments in workings might be a more or less temporary stabilization, a further period of imperceptible improvement of the slope opposed to other moments of aggravation, but without the actual risk of collapsing for at least another 300 years!

In 2011 the restoration of stone surfaces was completed, both inside and outside Steeple.

 

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