Large-scale survey method for the integrity of historical urban walls: application to the case of Volterra (Italy)

Several relevant collapses of historical urban walls happened in Tuscany in the last ten years, due to rainfalls. The wide extension of the walls, with difficulties of proper monitoring, joined with lack of maintenance, contributed to the failures. This recalled the attention on their vulnerability, in view to ensure a proper safety level and appropriate cultural heritage protection. In this paper, a method of extensive and quick structural survey to identify the mechanical characteristics of an historical urban wall path is proposed. It is based on geographic method of management of the territory (GIS database, satellite data). The data are obtained throughout a discretization of the walls in a wide set of vertical sections. A reduced subset of sections is directly surveyed, while the others are indirectly identified via numerical procedure, with the help of GIS data. A specific form to take note of the most relevant features is edited. The method is tested on the entire perimeter of the Middle Age walls of Volterra (2,6 km), affected by two relevant collapses in 2014. The procedure of survey is conceived to perform structural analysis to evaluate the vulnerability to landslides and earthquake risks, in view to determine restoration strategies and consolidation or monitoring programs.