GNGTS 2018 - 37° Convegno Nazionale

740 GNGTS 2018 S essione 3.3 Acuto test site: microseismic monitoring. Since 2015, an abandoned quarry located NE of the village of Acuto (Frosinone) has been individuated as test site for the installation of a multi-sensor monitoring system on a rock block prone to failure, to investigate the long-term rock mass deformations due to temperature, wind and rainfalls. The multi-sensor monitoring system consists in: 1 thermometer for the rock mass temperature; 6 strain-gauges installed on fractures of the rock mass; 4 extensimeters installed on open fractures; 1 optical device for the detection of rock fall events on a railway track posed to reproduce hazard scenarios and 2 weather stations, installed at foot and top of the slope wall, equipped with air-thermometer, hygrometer, pluviometer and anemometer for wind speed and direction (Fantini et al. , 2016). Several experimental activities have been carried out so far, in order to force the 12 m 3 protruding rock block (separated through a main open fracture from the back quarry wall) by thermal and dynamic actions to study inelastic strains induced by external actions (Fantini et al. , 2017). On February 23 th 2018, a microseismic monitoring system has been installed in order to study the vibrational behaviour of the protruding rock block and of the quarry rock wall. In particular, 6 one-component micro-accelerometers Brüel & Kjær type 8344 have been deployed along an horizontal alignment with a spacing of about 15 cm: in this configuration 3 sensors are placed on the rock block (ID: 1, 2, 3), 2 are located on the rock mass wall (ID: 5, 6) and the last one is positioned at the passage between the rock block and the rock mass wall (ID: 4) (Fig. 1). The sensors were connected to a datalogger SomatXR CX23-R of HBM, powered by a supply system constituted of a solar panel and a backup battery. The acquisition was set in continuous mode with a sampling frequency of 2400 Hz; data were periodically downloaded on site until the end of May 2018, when the microseismic monitoring was stopped. Data analysis. Microseismic events exceeding a user-defined threshold set at 0,001 g have been detected on the three-months dataset collected at Acuto. A typical microseismic event is characterised by a very short duration in time, spanning from 0.05 to 0.2 s, and a frequency content generally ranging from 80 to 500 Hz. The daily events detected are variable from 0 to several hundreds, with a concentration of the events in rainy days. With the aim of investigating Fig. 1 - Acuto quarry test site. The monitored sector of the quarry wall and the 12m 3 protruding rock block is shown in a); the squared area is zoomed in c), where positioning and ID of the accelerometers is reported; datalogger and power supply system (b).