Geophysical and geotechnical observations to assess the morphological risk in the Acqua Albule Basin sinkhole prone area (Rome, Italy): two case studies

Abstract

We present the results of multidisciplinary investigations of two significant sites, located in the Acque Albule Basin (AAB), 25 km Northeast of Rome (Italy). This basin has been interpreted as a transtensional structure, lying in the western margin of the Apennine range and affecting the Plio-Pleistocene sedimentary and volcanic sequences. During late Pleistocene times, AAB has been filled in with thermogenic travertine of variable thickness. Since historical time, lithoid travertine has been quarried, becoming the main building material during the Roman period (Lapis Tiburtinus). At present, the mining activity still represents the main economic resource of the region together with thermal baths. After the end of the II World War this area has experienced a strong urbanization and marshy lands were transformed into densely populated areas affected by subsidence and sinkhole phenomena. In order to characterize these environmental hazards from the geophysical and geotechnical point of view, we chose two test sites close to relevant anthropic infrastructures. Site A, located at the southern side of the Guidonia military airport and beside an important road; site B, a few kilometers South-East of site A, lies next to the Regina and Colonnelle Lakes and close to the Roma- Pescara railway. The former feature is a large sinkhole depression, hundreds of meters in width, characterized by ongoing subsidence, whereas the latter consists of two sinkholes actually acting as springs. Both sites lie in proximity of inferred faults, which would affect the AAB in the N-S and NE-SW– directions respectively. The aim of this study is to compare the two cases by collecting geological, geomorphological and geophysical parameters and thus testing the variable controlling their formation and development. We also extended the geophysical campaign in the surrounding area using a multidisciplinary approach to image both surface and subsurface features. We carried out stratigraphic and geomorphological survey, 2 and 3D Geoelectrical Tomography (ERT), differential GPS altimetry, gravity, magnetic, seismic, and soil gas measurements. Moreover, two drillings have been bored inside and outside the depression area of the Site A, reaching depths of 60 and 20 meter, respectively. Geotechnical parameters of the recovered stratigraphy were also measured by laboratory tests. In general, the approach we propose could provide key elements to recognize similar situations in sinkhole prone areas. Moreover, comparative analysis together with the monitoring of the A site can represent useful tools to understand the genesis and dynamics of phenomena and hopefully to forecast their evolution, particularly in the parts of the basin where active movements caused fractures and damages to buildings and infrastructures.