Role of Monitoring in Historical Building Restoration: The Case of Leaning Tower of Pisa

A short summary is presented of the studies and the actions of Committees appointed in past 50 years for the Tower of Pisa. The discussion first addresses the attempts carried out during the whole history of the Tower to measure its movements and the efforts made to understand the origin and causes of its inclination. A history of foundation rotation has been also deduced by means of a precise architectural survey, which has led to a diagnosis for the inclination and its increase in time. As a consequence, several hypotheses for its stabilization have been proposed. All the measures for leaning tower stabilization need the application of observational method for their implementation. The observational method is strictly based on a comprehensive monitoring system, both described in the second part of the paper. The aims are to stress the importance of a well-conceived monitoring system and to propose the extension of concept of monitoring to construction history details. The data and actions described are from the work carried out by committees appointed by Italian Government during the second half of 20th century, in particular by the committee chaired by Professor Jamiolkowski, appointed in 1991. The authors have collaborated with this committee since 1993, and they are still in charge of the monitoring and maintenance of the Tower of Pisa.