Impact of environmental stressors on jointed rock cliffs by acoustic emission sensing. Preliminary findings from the Acuto Field Laboratory (Central Italy)

Seasonal variations in natural environmental stressors represent preparatory factors of rock block deformation driving to failure on slopes as well as on underground contexts. To better assess the role of the environmental stressor regarding the rock slope stability, the present study focused on monitoring an unstable rock block cropping out in a quarry wall at the Acuto field laboratory (Italy), through a methodology for a high-resolution detection of acoustic emission (AE) signals, their characterization and correlation with the concomitant environmental stressors has been developed. Through the spectral analysis of the AE waveforms, the seasonal distribution of average frequencies varies significantly, and the main frequency band was 0-200 kHz. The two-step clustering method and frequency characteristics were used to initially identify group "I" as microcracks-related AE events. The identification results using the MLP neural network showed that microcracks-related AE events accounted for only 23.2% of the total monitoring cycle. This percentage rises to 51.1% and 55.2% for the periods May to December and December to February 2024, respectively, as the rainy season tapers off. The power-law index of AE event energy is variable in the considered time windows in which the monitoring was carried out. Results of a comparative statistic indicate a joining between high AE rates and cooling-relaxation processes, as well as a weak correlation among the waveform attributes and meteorological stressors. The power-law index of AE event energy decreases during the cooler months, particularly from July to December, correlating with the overall drop in temperature. During this period, the few high-energy events can be considered potential indicators of geological hazards.An identification model for acoustic emission events based on two-step clustering and neural network is established.A link between high acoustic emission rates and cooling-relaxation processes was found.Seasonal variations in rock block stability were judged based on power-law indexes.