Destined to collapse with the passing
of time, a solution to the mystery may now have been found.
Leaning Tower of Pisa, one of the Seven Marvels of our times,
is famous for its five-degree tilt from the vertical, so that
the top hangs around 4 metres over the base. The Tower first began
to lean southwards at the end of the 12th century, when work on
the fourth storey was under way, and over the centuries the building
has sunk 3 metres in the ground. The entire area is in fact subject
to a gradual subsidence of the soil and the ground underneath
is like a water reservoir, given the proximity of the sea, which
has since moved back and is now at a distance of over six miles
from the town. Work
was interrupted and then resumed around a century later. When
the seventh circular storey was reached the Tower subsided again,
making further building impossible. Finally, thanks to a correction
to the top part of the building by means of an artifice still
visible to the naked eye, almost 200 years after the foundations
were laid the belfry was completed.
the Tower continued to subside, rotating by 1.2 millimetres per
year, in 1990 an international committee of prominent experts
was called in to save the world’s most famous bell tower.
Tower seemed fated to collapse because of the nature of the soil,
composed of marine and river sediments, and also because of the
strain on the building due to its inclination. The problem was
so complex it required ten years of studies. Scientific tests
revealed the risk of breakage at the level of the first cornice,
under special stress, and plastic-coated steel cables 15 millimetres
in diameter were wrapped around the critical point to prevent
further widening of the cracks and maintain the integrity of the
reduce the lean, in 1993 a circular girder supporting a series
of weights, sixty lead ingots weighing 10 tons each, was installed
on the north side to counterbalance the inclination: the Tower
was saved, but a state-of-the-art monitoring system capable of
receiving up to 220 different signals every 5 minutes was set
up to keep it constantly under control.
lingot strategy made it possible, for the first time in history,
to stop and actually reduce by a centimetre the inclination of
the Tower. At this point it became necessary to intervene exploiting
the same balancing principle but eliminating the visual impact
of the lead weights. A
system of anchorages
positioned at a depth of up to 45 metres was fixed to a concrete
ring, this time located below the ground.
work on the underground ring proceeded on the north side, to the
south and the east experts were forced to pump liquid nitrogen
into the ground to freeze the earth.
disaster struck: the Tower’s inclination suddenly increased and
another 270 tons of lead had to be placed on the north side. The
project was abandoned. Once the danger had passed, a definitive
solution was found: the soil extraction method, involving the
gradual removal of soil from under the north side of the Tower,
causing it to subside a little and counterbalance the south side.
To strengthen the structure, cement was injected in the masonry
and slim steel rods were inserted.
rods were used to secure the Tower, forming a sort of “lasso”
that would tighten around the body of the building in case of
danger. In 1999 soil extraction began: 41 drills gradually removed
38 cubic metres of soil and the Tower was moved back half a degree,
crucial for its stability.
lead weights, the circular girder, drills and tie rods, being
no longer needed, were dismantled one by one. In 2001 the Tower
was opened to the public, but the restoration of its stonework
is yet to be completed.
The next step was to
measure the temperature of the stone in different seasons of the
years, observe the effect of the wind, monitor alterations caused
by pollution and the presence of plants and lichen and even analyse
the course of rainwater inside the building.
order, update and compare all the data gathered in years of studies
the Scuola Normale di Pisa, subsidised by the European Community,
has created a special data processing system called Akira that
provides a perfect picture of the whole Tower, stone by stone,
using state-of-the-art technology. Work on the Tower’s masonry
began in July 2000, under the supervision of the Central Institute
of Restoration, and is expected to be completed in 2006.
order to keep the Tower open to the public, an innovative scaffolding
runs up the building without touching the marble surface, like
an external lift, so that work can be carried out on only a single
storey at a time, leaving the monument and its restoration exposed
to the curious gaze of tourists.