The game of the slopes

Pisa to study - Ulisse

It was destined to collapse over time. Perhaps now you have found the solution to the mystery. The Tower, one of the Seven Wonders, is famous for its gradient, more than 5 degrees, pokes the top about 4 feet from the base. The building collapsed during the centuries up to 3 meters, began to lean towards the south at the end of the twelfth century, when the building was reached only at the fourth order. The whole area was in fact subject to a progressive lowering of the ground and the ground was like a water tank on the immediate proximity to the sea which has since gone more than 6 miles from the city. Work stopped and then resumed about a century later came the seventh ring, but again gave way and prevented the Bell Tower to continue. Only after almost two hundred years since the first stone, correct the highest part of the structure with an artifact is still visible to the naked eye, they completed the belfry. In 1990, while turning the tower continued to sink about 1.2 mm per year, an international committee of high-level expert is called to deal with the world's most famous bell tower. The tower seems to be destined to collapse because of the nature of the soil consists of marine and river sediments, and for the stresses caused by tilting the structure itself. The complexity of problems requires ten years of study. Scientific analysis shows the risk of rupture at the first frame, as stressed by the slope, and is made a "hoop": steel cables of 15 mm in diameter, insulated by a protective sheath, are narrow around the critical point for against the enlargement of the slots, ensuring consistency to the wall. Against the grain, in 1993, installed on the north wall is a ring beam to support a series of "weights", sixty lead ingots of 10 tons each, placed at the counter slope: The Tower is safe but is guarded by a sophisticated monitoring system able to receive every 5 minutes up to 220 different signals. With the strategy of ingots, for the first time in history, the Tower of stops and reduces its slope an inch. You now need an operation that exploits the same principle of balance but eliminate the visual impact of the seals. A system of anchors placed up to 45 meters of depth is fixed to a concrete ring, this time placed in the ground. The construction goes underground on the north side of the ring and to intervene in the south and east of the experts were forced to freeze the ground with the introduction of liquid nitrogen. But the situation falls: the tower tilts sharply and you have to place additional 270 tons of lead in the north, abandoning the project. Averted the danger, then the winning answer is: the "sottoescavazione", that is a controlled removal of land causing a collapse of its financial statements to the north tower on the south side. Consolidated through the masonry in the critical areas of special mortars injections and the insertion of thin stainless steel bars, after assuring the Campanile with the Wind Bracing, ie a "lasso" that in case of danger squeezing around his body, in 1999, shall sottoescavazione: forty drills gradually remove 38 cubic meters of land and the tower that fetches half a degree Indispensable to its stability. Leads, ring beam, drills and Bracing, completed their task, they are dismantled, one by one. In 2001 the bell tower was reopened to the public but must still undergo the restoration of surfaces. Now is the time to measure the temperature of the stone with the changing seasons, to observe the action of the winds, to control pollution and alterations caused by the presence of plants and lichens, to analyze even the route taken by rainwater to 'inside of the building. To order, update, and compare data collected in years of studies, the Scuola Normale Superiore in Pisa, with the help of the European Community, a dedicated computer system designs, Akira, who with the use of advanced technologies, allows you to map the entire tower stone by stone, to degradation degradation. The intervention on surfaces, began in July 2000 under the leadership of the Central Institute for Restoration, is expected to be completed in 2006. Accessible to leave the Tower has been designed an innovative scaffolding, without touching the marbles, running as an external lift and can be used on one order at a time, allowing the gaze of curious tourists, the monument and its restoration.
Lucia Capitani