Landslide analysis of historical urban walls due to rainfalls: overview of recent collapses in Italy and the case of Volterra

This work arises from the evidences of recent collapses of historical urban walls. These events, mainly occurred after severe rainfalls, recalled the attention on the vulnerability of these infrastructures. Specific evaluation models which take into account the role of moisture inside the walls are not frequent in the literature. The problem is difficult to treat in many practical cases due to the extension of the urban walls and the variability of their geometry and of their mechanical features. The integrity of the urban walls is investigated throughout the analysis of a set of vertical sections. Risk scenarios of rainfall events are analyzed. At this scope, four limit states are proposed and investigated to determine both collapse and serviceability conditions. The combined risk analysis is obtained by treating the single-risk analysis. The results from the limit analysis are compared with those from the finite element method models. The method is applied to the relevant case study of the Volterra historical urban walls with a retrospective analysis of the section that collapsed in January 2014 and the analysis of other relevant sections.