Preserving Pisa's Treasure

by John Burland,
Michele Jamiolkowski,
Carlo Vigginai,

Serial Information: Civil Engineering—ASCE, 2002, Vol. 72, Issue 3, Pg. 42-49

Document Type: Feature article


Pisa's bell tower, a prime example of Romanesque architecture, would be renowned even if it did not lean. Construction of the tower began in 1173 and was not completed until almost 200 years later, in 1370. Founded on weak, highly compressible soils, the tower's famous inclination eventually reached the point where it exhibited leaning instability. By 1990, the rate of tilt was equivalent to a horizontal movement at the top of about 1.5 mm per year. Temporary stabilization of the structure was achieved by applying lead weights to the north side of the tower. After considering various options for more permanent stabilization, engineers settled on a process of soil extraction, in which small amounts of soil were slowly and carefully removed from selected areas beneath the tower's foundation. Currently, the tower exhibits the angle of inclination in had in 1838. The tower was reopened to the public in December 2001.

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