Distinct Element Method Analyses for Damage Assessment: The Case of the Valverde Bulwark in the Venetian Fortress of Bergamo

The 16th-century Venetian Fortress of Bergamo is a complex defensive system over 5 km long with more than 70,000 m2 of masonry wall facing, inscribed to the UNESCO world heritage list in 2017. Today, the first causes of its deterioration are the vegetation growth and the lack of maintenance that have led to instabilities and local failures, particularly in the north-west portion. Thus, in 2019 and 2020, survey campaigns were carried out to assess the safety of one of the most damaged sections, the Valverde bulwark. The survey combines on-site observations, laboratory tests, and photogrammetric and laser scanner surveys to describe the state of the bulwark. Some numerical simulations have been performed within a Distinct Element Approach (DEM). DEM has been conceived for geo-mechanical analysis, such as caves or mines; however, several researchers have widely proven its application to masonry structures. It assimilates the masonry to a system of discrete bodies consisting of blocks (usually rigid) interacting on their interfaces. DEM analyses are usually executed on simplified models, rarely considering the actual geometry of the masonry structure due to the extremely time-consuming and the usual lack of information. Within the research, a routine dedicated to defining a real-like geometrical model has been developed. The numerical analyses were run to understand the condition of the Valverde bulwark in the actual state, analysing the conditions under self-weight and earth pressure and the behaviour under seismic loading. Through the detailed survey and its automatic digitisation, it is possible to fully recognise and analyse the state of health of these historical structures as well as their mechanical behaviour.