Advanced applications of geoscience technologies for monitoring and modelling of slope instability in cultural heritage sites

The uniqueness of the elements at risk and the need of developing non invasive methods suitable for on site diagnostic activities are increasingly encouraging the employment of remote sensing technologies and novel monitoring instrumentation, which could efficiently support detection and prevention of landsliding events potentially damaging cultural heritage sites. Monuments preserved for centuries have being exposed to chronic conservation issues due to particular geographic location and geological nature of foundation ground, and the current condition could suggest the execution of urgent stabilization interventions. Deterioration patterns visible on the surfaces of masonries are commonly a reliable element testifying the temporal and spatial evolution of active instability mechanisms or reactivation/acceleration of dormant/past processes. Specific analysis of the structural relationships between the foundation ground and the historic buildings represents the key point of a multidimensional and multidisciplinary investigation. Monitoring campaigns and numerical modelling can also contribute to the understanding of the kinetics of instability mechanisms. This work illustrates the potentials of advanced geosciences technologies in the field of conservation of cultural heritage, both entire sites and single monuments, as specifically tested during the most recent experimentations by the research unit of the Department of Earth Science, University of Firenze, devoted to the development of integrated approaches for spatial and temporal characterization of landsliding hazard threatening cultural contexts. Among the tested monitoring instrumentation, the Ground-Based Interferometric Sythetic Aperture Radar (GB-InSAR) was successfully transferred to the field of structural analysis. It was demonstrated its suitability both as real-time monitoring device at high sampling frequency and optimal spatial resolution and surveillance system for preventive activities on archaeological monuments affected by deformation movements. Combining GB-InSAR data with terrestrial laser scanner (TLS) 3D models of the monitored monuments allowed us precise localization of the ongoing deformations, clarifying the structural behaviour of the masonries and consequently guiding on site surveys of the local conservators to verify the real condition of the structures. Long-range TLS was also implemented for obtaining meshes representing the outcropping surfaces of the foundation substratum of historic hilltop towns affected by rock mass instability. Innovative procedures for semi-automatic extraction of rock mass discontinuities were developed and validated on different case studies. ‘Site specific’ kinematic analyses were performed to identify the most critical rock-wall sectors, prone to be interested by block/flexural toppling and plane/wedge failure. Such high detailed analyses of the rock masses and the related classifications in terms of risk classes, as well as crack pattern surveys of the overlying historic masonries, constituted the knowledge basis for planning the installation of on site monitoring network systems. The analysis of the monitoring data, continuously collected by means of on site devices (e.g., crack gauges, tiltmeters, meteorological station), was exploited for assessing the evolution of instability processes, jointly to the evidences from deep ground investigations and laboratory tests. As final outcome of all the discussed experimentations, local landsliding hazard factors were examined and the effectiveness of the geosciences technologies adopted was evaluated in terms of real contribution in designing consolidation works of the unstable substratum and planning of restoration interventions of the damaged cultural heritage.