Stabilising the Leaning Tower of Pisa: the Evolution of Geotechnical Solutions

Abstract

On Thursday 7 September 1995 ground freezing was being carried out around the Tower of Pisa when it began to increase its inclination dramatically. In one night, it moved southwards more than it would normally have moved in a year. The freezing operation had to be terminated and for three weeks desperate efforts were made to save the tower. This period has come to be known as Black September. The paper describes how and why the Pisa Commission got into this predicament and how it was resolved. More generally the paper traces the evolution of some of the ideas and schemes for stabilising the tower that were put forward by members of the Commission. Unravelling the history of the tower and understanding the mechanisms of its movement proved crucial to developing the successful stabilisation measures. A detailed technical description of the project is given by Burland et al.1