Preliminary results of vibration modes induced by forced dy-namic shaking in a quarry rock wall

Rockslides are one of the most hazardous natural events, because of their velocity and rarely detectable precursors. Possible strategies to prevent the risk associated to these events consist in: a) studying the gradual creep-driven deformation of rock mass by setting a proper monitoring system (Loew et al. 2016); b) realizing numerical models also considering progressive failure of rock slopes (Eberhardt et al. 2004); c) coupling microseismic monitoring systems and numerical models, taking in account rock mass damage during time (Xu et al. 2014; Tang et al. 2015); d) analyzing variations of ambient noise as indicators of imminent failure (Got et al. 2010; Lévy et al. 2010). To investigate long term rock mass deformations due to temperature, wind and rainfalls, the abandoned Acuto quarry rock wall (Frosinone – Central Italy) was selected in Autumn 2015 as test site for the installation of a multi-sensor monitoring system on a rock block prone to failure. The experimental site is included in the carbonatic Monti Ernici ridge. More in particular, Mesozoic wackestone with rudists crops out on the sub-vertical quarry wall with a height ranging from 15 m up to 50 m (Accordi et al. 1986). A geomechanical characterization of the rock mass led to the recognition of four joint sets, here indicated according to dip direction/dip convention: S0 (130/13) corresponding to the limestone strata, S1 (270/74), S2 (355/62) and S3 (190/64) (Fantini et al. 2016). The monitored sector is located in the NW portion of the 500 m long quarry front, which is characterized by the presence of a 64 m3 densely cracked protruding block, separated from the back quarry wall by a main fracture. The multi-sensor monitoring system consists in two weather stations with air-thermometer, hygrometer, pluviometer and anemometer for wind speed and direction, installed at foot and top of the slope wall, one thermometer for the rock mass temperature, six strain-gauges installed on micro-fractures of the rock mass, four extensimeter installed on open fractures and one optical device.