Structural Behaviour of the Leaning Tower, Pisa

The Tower of Pisa is well known for its architectural grace and its harmonious presence among the monuments of Piazza dei Miracoli, but above all it is known for its inclination, which makes it unique in the world. It is clear that this inclination is not caused by structural faults in elevation but rather by problems in the foundation-soil. Indeed, the inclination is due to progressive settlement in the soil under excessive loads, and the soil's particular characteristics on the surface and at depth. This situation, which will here be concisely illustrated, was only brought to light in the years 1984-87. An important research assessment of the Tower's structure carried out with sophisticated techniques obtained experimental data and information about the structure by means of television cameras placed in specially drilled holes.