ANCIENT ROME UNDERGROUND QUARRY NETWORK AND THREAT TO INFRASTRUCTURES AND LIFELINES OF THE CITY: RECENT CASE STUDIES

We present the results of our first response interventions for site assessment and mapping of sudden collapses of paved streets sections above ancient underground quarries in Rome, Italy. Underneath Rome there is an extensive network of “pozzolana” quarries excavated to mine the pyroclastic products of the Alban Hills and Monti Sabatini volcanoes (mid-Pleistocene to early Holocene). The quarrying started as early as the VIII century BC and continued for centuries to provide the main components for Roman masonry. The undergrounds quarries are estimated to cover a surface of tens of km² but a significant part of this network is yet to be mapped. On average, the quarries are found at depths ranging from 7 to over 20 meters below the walking surface of the city.

As Rome grew, it developed into the areas above the quarries. Today, in many of these areas multi-story building foundations discharge their weight onto the quarries’ supporting pilons. The utility lines carrying water, gas and sewage are buried below street level above the quarries, and run parallel to the streets. Vibrations generated by the transiting vehicles effects the integrity of these lines; the continuous stress generates microfracturing of the conduits that may result in leakage of fluid content. The fluid buid-up from the leak interacts with the ground producing slurry that acts as an effective erosional agent weakening the roof of the underlying quarry. This may lead to a collapse of the surface, while filling with rocks, soils and anthropogenic material the underground cavity and producing a hole at street level. These collapses are becoming increasingly common, as of mid-2013, 67 street collapses and 8 other related mass wasting episodes have been observed, 77 in 2012 and 44 in 2011.

Our interventions, requested by the Municipality of Rome and the ministry for Civil Protection, are aimed to produce 1 - A highly detailed stratigraphy of the materials involved in the collapse; 2 - updated mapping of the underground quarry at the site, its relationship with the surface and lateral developments; 3 – an in depth analysis of the relationships among involved materials and their structural characteristics for hazard assessment and mitigation purposes. Examples from 3 sites, Via Columella, Tor Fiscale and Piazza Lodi will be presented.