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

The 16th century Venetian Fortress, with more than 70,000 m2 of masonry wall facing, characterises the city landscape of Bergamo. Almost intact and well preserved, the defensive system was inscribed on the UNESCO World Heritage List in 2017. Today, the first causes of its deterioration are the vegetation growth and the lack of maintenance, which have led to instabilities and local failures, particularly in the northwest 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 bulwark. Numerical simulations have been performed using a distinct element approach, i.e. assimilating the masonry to a system of discrete bodies consisting of blocks (usually rigid) interacting on their interfaces. A routine dedicated to defining a real-like geometrical model has been developed. The numerical analyses were run to assess the conditions of the Valverde bulwark under self-weight and earth pressure and considering seismic load. Through the detailed survey and its automatic digitisation, it is possible to fully recognise and analyse the state of health of these historic structures and their mechanical behaviour