TEMPERATURE CHANGES ANALYSIS IN JOINTED ROCK MASS TO INVESTIGATE EFFECTS DRIVING SLOPE INSTABILITIES AT THE ACUTO FIELD LABORATORY (ITALY)

The understanding of thermo-mechanical strain effects in charge of natural and man-made rock slopes is strongly conditioned by the nature and distribution of transient thermal input as well as on the rock matrix and fracture mechanics.

While the subcritical crack growth mechanics and stress-strain relationship due to periodic or transient stressors in rocks are adequately investigated by monitoring and laboratory approaches, the evaluation and prediction of timing and location of the ultimate rock failure in extended rock cliffs are to date less focused.

Despite non-trivial, the understanding of the size and location of incipient failure along wide and high rock cliffs is an important target to mitigate the geological risk related to infrastructures and natural or cultural heritage. To address this research topic an integrated investigation encompassing geotechnical and geophysical monitoring, IRT remote sensing, as well as numerical modelling are carried out since 2016, availing of an abandoned quarry in Central Italy nowadays became the Acuto Field-Lab.

The research focused on: i) full monitoring of weather conditions and rock strain acquisition by strain gauges and jointmeters; ii) 3D thermal monitoring and numerical modelling of temperature changes over the rock surface and across joints; iii) geophysical detection by seismic noise of permanent changes in physical and mechanical parameters and MS event detection as precursors of incipient failures; iv) statistical quantification of inelastic deformation in rock mass and ANN-based prediction of cause-to-effect relationships among different environmental stressors and induced strain.

The main outcomes focused and highlighted the importance of joint set attitude and location in controlling temperature distribution both at the daily and seasonal timescales. The thermomechanical analysis allowed to characterize the cyclic contraction and relaxation response of major rock fractures and microcracks to the experience temperature fluctuations under both recurrent conditions and a non-ordinary weather event, showing, as preliminary results, low-frequency MS signals attributed to different driving mechanisms under subcritical and critical regimes as consequence either by thermal dilation and contraction or by freezing-thawing mechanisms. In this perspective, newly deployed AE-sensors and a dedicated FBG- array will respectively broaden the frequency band and the level of observation in jointed rock masses opening new scenarios for thermomechanical studies.