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Leaning Tower of Pisa: Behaviour after Stabilization Operations

John B. Burland, Michele B. Jamiolkowski, Carlo Viggiani
International Journal of Geoengineering Case Histories, 1 (3), 156-169

It is well known that the foundations of the Leaning Tower of Pisa were stabilised using
the method of underexcavation to reduce the southward inclination of the Tower by
about 10 percent in combination with controlling the seasonally fluctuating water table
beneath the north side. Having been closed to the public since early in 1990, the Tower
was re-opened in December 2001. The paper summarises the response of the Tower
during the period of implementation of the stabilisation works. Monitoring of the
movements of the Tower has been continuing and the observations obtained since 2001
are presented. It is shown that over the six years between 2003 and 2008 the induced
rate of northward rotation of the Tower has been steadily reducing to less than 0.2 arc
seconds per year. Similarly the rate of induced settlement of the centre of the
foundation has been steadily reducing and is approaching the background rate of
settlement of the Piazza. Piezometer measurements close to the north side of the
foundation shows that the drainage system has been successful in stabilising the
groundwater levels beneath the north side of the Tower’s foundation. The paper
concludes with a brief discussion on the possible future behaviour of the Tower.

Case histories: soil-structure interaction and preservation works