Application of an integrated monitoring system for rock failures in the Coroglio tuff cliff (Naples, Italy)

In high risk, coastal, urban areas, cliff stability monitoring is an essential task for human activities. This paper presents the implementation of an integrated monitoring system at the Coroglio tuff cliff, located in the highly urbanized coastal area of Naples (Italy) on the border of the active volcanic caldera of Campi Flegrei. The system consists of standard geotechnical monitoring instruments (crackmeters and clinometers) coupled with a modern deformation monitoring technique based on Brillouin Optical Time-Domain Analysis (BOTDA) optical fiber network, integrated by a velocimetry sensor and a weather station. Remote sensing equipment like UAV digital photogrammetry (UAV-DP) and terrestrial laser scanning (TLS) have been also used for obtaining detailed multitemporal DTM of the cliff, as well as geostructural analysis and classification of the slope, supported by structural fieldwork. In the first phase of the study, we integrated the results of long-range TLS surveys with structural field mapping. The accurate and rapid detection of structural discontinuities of the rock played an important role for the understanding of the failure mechanism and the kinematic analysis of unstable blocks along the cliff. The preliminary results obtained during the first two year of monitoring activity (2014-2015) are presented. Micro-deformation of rocks measured by geotechnical sensors reveals a general sinusoidal trend, possibly linked to the bulk volume variation of the rocks, as a response to seasonal and daily temperature variations. This research provides a contribute to the understanding of the rates of geomorphic evolution of coastal tuff cliff and its relation with forcing factors (e.g. meteo-marine weathering, human actions, volcano-tectonic activity) in the perspective of early-warning actions and policies.