Abstract

The historical centre of the city of Naples is characterised by a network of underground anthropogenic cavities. Most of these cavities are stable and safe but sometimes for several reasons they are at least partially responsible of the occurrence of instability phenomena such as sinkholes and collapses. The opening of a sinkhole in the cloister of the Ancient Royal Boarding School (known as Educandato Reale of San Marcellino) led to fears of instability in the known underlying cavities. Therefore, a site investigation program was carried out to ascertain the causes of the event. The investigation concluded that the sinkhole was not related to the underneath cavities, located in tuff between 12 and 20 m beneath the main building. Nevertheless, due to the interest raised by the preliminary safety assessment, such a cavity system was selected within the MOSCAS project for further studies. The results of the site investigations and the stability of the cavities determined via FEM code Plaxis 2D are presented and discussed in this paper.

Introduction

Urban cavities that originate from human activity are excavated for several reasons (quarries, cisterns, crypts and catacombs); these cavities often form an intricate network of tunnels underneath urban centres, sometimes forming systems with several levels (Berti et al., 2002; Nisio et al., 2007).

The presence of anthropogenic cavities in the subsoil of urban centres can cause the collapse of the most superficial portions of the ground with the formation of surface collapses, creating a serious risk for urban buildings. In recent years, there has been an increase in the number of cases of sudden collapse, especially in urban centres, where cavities, sometimes combined with possible leaks in the hydraulic network, facilitate the triggering of these phenomena.

Within the framework of the MOSCAS research project (Models and tools for the characterization of underground cavities), safety levels of the cavities underneath the historic building of San Marcellino in the city centre of Napoli, Italy, was assessed. The interest for this case study was raised by the opening of a sinkhole in the cloister of the building in April 2012, that led to concern of possible instability in the known underlying cavities.

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