An update on the Tower of Pisa

The Leaning Tower of Pisa has been stabilised in the years 1999–2000 by an International Committee appointed by the Italian Government. An analysis of the whole history of the monument, starting from its construction in the XII century and including the results of the modern monitoring of XIX and XX century led the Committee to the conclusion that the Tower is affected by a phenomenon of instability of the equilibrium, depending on the deformability and not on the strength of the foundation soils. The stabilisation intervention, totally respectful of the integrity of the monument, consisted in slightly decreasing the inclination of the Tower by underexcavating a small volume of soil beneath the north side of the foundation. The paper briefly reports the analysis and the intervention; the observation of the behaviour in the twenty years elapsed since then allows some preliminary evaluation of the future behaviour.