Throughout the monuments history, architects and engineers have attempted to halt the lean, but since regular monitoring began in 1911, the offset(偏移) at the top of the tower has increased at a fairly consistent rate of about 1.2 millimeters each year. Today the top of the tower is 5.227 meters off-center, visibly leaning south. Fears about the safety of the landmark became acute when a similarly constructed bell tower at the Cathedral at Pavia collapsed suddenly in 1989. Shortly thereafter, the tower at Pisa was closed to visitors.
In 1990, a special commission, composed of Italian and foreign experts in the fields of structural engineering, geotechnical engineering, history of art and restoration of monuments, was brought together by the Italian government to determine new ways to save the tower. The Tower of Pisa Project Consortium has supervised several projects that have stabilized the structure and slowed the rater of its incline.
Initial efforts focused on the exterior of the tower, but in the next few months, other, more radical techniques will be tried to halt the towers lean. There methods will be applied directly to the soil, modifying the towers footing. Large-scale filed trials are now under way at the Miracle Square, where the tower stands, but all work is being done far from the monument itself to guard against the possibility that altering the ground too close to the tower could eventually damage the building.
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