Hazard Assessment and Mitigation associated with the presence of man-made underground cavities in highly urbanized areas

Most of the subsoil of the municipalities located north of the city of Naples is characterized by the presence of numerous cavities of anthropogenic origin The cavities located immediately below the upper surface of the Neapolitan yellow tuff banks were created to quarry the stone material needed for masonry construction above it. Subsequently to the extraction of the stone material, the cavities were regularly used to store various materials, and because of the constant rate of humidity, they were especially suitable for the preservation of foodstuffs. Though structural instability has increased over the years, the cavities have remained intact for many centuries despite the surrounding geological forces. This fact may be due to the particular chemical and physical properties of the more superficial layers of the subsoil up to the upper base of the tufa formations. This material can be defined as loose pyroclastic products with inter-particle bonding so strong so as to almost completely counter balance the thrust of the land. However, the chemical and physical bonds and the resulting cohesion tend to weaken considerably when the water content in the soils changes significantly, due to water pipe and/or sewage network damage, and the ground becomes saturated. Research carried out on a portion of the heavily urbanized territory has suggested serious hydrogeological risk of concern to the increasing population. A general geological-geomorphological, geological-structural, hydrogeologic and seismic analysis was performed on the area through geophysical prospecting and the acquisition of information with remote sensing and satellite procedures.