Integrated active and passive geophysical methods to explore underground soils in urban scenarios: the case of "Stampace alto" in Cagliari (Italy)

The integration of active and passive geophysical methods is essential to explore the underground structures in complex urbanized contexts, frequently characterized by the presence of buried archaeological structures and artificial voids. The study area is located in a historical district of Cagliari (southern Sardinia, Italy). This was addressed to the construction of new buildings after the demolition of previous old and dilapidated structures. Despite that, the area was classified as a site with significant archaeological potential because of the numerous discoveries that occurred in the surroundings during several excavations and technical dugs for urban and road maintenance works. The exploration approach consists of the combination of 2D Electrical Resistivity Tomography and gravimetric surveys, to identify the spatial position and the geometric features of potential underground voids and other buried manmade structures. 26 ERT profiles and 180 gravimetric stations have been distributed on the free surface of 4,000 m 2 . In the general experimental framework, the results of the low-invasive investigations have been correlated to the geological knowledge from direct surveys. The integrated geophysical approach has provided both qualitative and quantitative data for a preliminary definition of the underground geological model of the site. This study suggests that the extensive use of non-destructive methods can orient urban planning strategies in historical towns by retrieving three-dimensional spatial models of foundation soils.